Hollow World
by Veldeia
Summary: The 10th Doctor and Martha, stuck in a cave, utterly unprepared and separated from the TARDIS - what else could go wrong?
1. The Chasm

**Author's Note: **As everyone who's been reading my stuff before well knows, I'm a hurt/comfort freak. I'm also totally in love with the 10th Doctor. Thus, here we have yet another cliched and unoriginal h/c story where he's in a world of trouble, this time in a cave, with Martha Jones. The story takes place in the 3rd season, before Blink. Be warned: this is a real WIP, not an "already finished, posting one chapter at a time" thing, like the stuff I've posted before this.

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**1. The Chasm**

"Ah, here we are! The Sixties! The Age of Aquarius! Peace, love and understanding, and men on the Moon!"

"Not barefoot, though," Martha said, with a wink.

"Hmm." The Doctor grinned smugly. "Not in several decades, no. Still, an exciting time! Come on, let's go!"

Still facing Martha, he backed away through the doors. After a few steps, he gave a surprised and rather alarmed "Oh!" and disappeared from view.

Unable to understand what exactly had happened, Martha rushed towards him. The moment she was out of the TARDIS, she saw something was wrong. Except for the light shining out through the windows of the police box, it was pitch dark everywhere around them. She couldn't make out any walls. The floor, or ground, under her feet was stone, and just a few paces in front of her, it ended in darkness.

"Doctor?"

"I could use a hand here, preferably two," came the answer in an uncharacteristically timid voice.

Martha could just see the tips of the Doctor's fingers where he was clinging to the ledge. Slowly, cautiously, she moved closer and crouched to the ground, taking in the situation. There was no knowing how deep the dark pit beneath him was. Obviously his hold was far from firm, because he hadn't even suggested that she could go back to the TARDIS for rope.

She clutched one of his hands between both of hers, muttering, "All right, all right. I've got you. Easy does it," as much for her own comfort as for his.

He loosened his grip of the edge, grasping her hands. "Careful, I'm not quite as light as I look, and the ground's slippery," he said.

It was obvious that she couldn't actually pull him up. She was sitting on the ground and leaning backwards, and his weight still threatened to drag her over the edge. She tried to dig her heels into the ground, but it was solid rock. Luckily, what help she could provide was enough that he was able to move his other hand, to get a better grip of the edge, and support more of his weight himself.

"Okay, have you got a proper hold now?" she asked.

"Yup, hanging on. No footholds, though. So, now, on count of three... One, two, three."

She heaved with everything she'd got, and he did his best to pull himself up. He managed to get one elbow over the edge, then the other, looking up at her with a very strained smile on his lips, but then, she heard the most terrible sound. She'd seen documents about the Polar regions, and she'd heard the sound of ice falling apart. This crack was somewhat similar, but even more grinding.

"No, no, no, no, no! Martha, watch out! Stand back!" the Doctor shouted, but it was too late.

The ground beneath their feet was moving, the part of the ledge they'd been standing on crumbling under their combined weight and the stress put on it by their struggle. Martha felt herself sinking, and she couldn't hold her balance. With one hand, she still clung to the Doctor's, with the other, she tried to reach for a handhold, a solid part of the ledge, the doorstep of the TARDIS, a rock, anything, but it was no good. There was nothing she could do.

They fell.

In a way, they were in luck. Instead of an endless free fall into the abyss, they hit the ground so soon that it was almost anticlimactic. Of course, it wasn't level ground. Even though the cliff face was no longer vertical, it was still very steep, and extremely slippery. Martha couldn't find a footing, but kept tumbling downhill, as did the Doctor. His hand slipped from hers.

She knew that trying to grab at everything around her would only make things worse, so she gave in to gravity, doing her best to relax, as absurd as the thought was. She couldn't tell how long they fell, but it felt like a very long time, first sliding, then rolling on the surprisingly smooth surface, every now and then scraped and pummelled by rocks, until finally, after what must've been at least a hundred feet, the ground levelled out.

She was too dazed to do anything to stop herself, so she kept going round and round until the momentum died away. Once she had come to a halt, she just lay there, waiting for her racing pulse to settle, so shocked and so amazed to be alive that she could barely feel anything at all.

After a few minutes, she had calmed down enough to be actually able to think. She could feel the pains of a dozen bumps and bruises, but nothing really bad. Tentatively, she tried moving each limb. Her right wrist protested strongly. Hissing at the pain, she probed it with her other hand. It was swollen, most likely sprained, but not broken. She could barely believe that was the worst of it. Her head was spinning and she was covered in dirt and aching all over, but incredibly enough, she had survived the fall without any major injuries.

She tried opening her eyes. She couldn't see a thing. The darkness was perfect, exactly like it had been around the light of the TARDIS. She was sure the police box hadn't fallen down with them, but looking up, she saw no trace of that glow. It was eerily silent as well - there was nothing but the soft sound of dripping water.

The relief of having survived the fall quickly gave way to an entirely new dread. She had never really been afraid of the dark, but this wasn't like any darkness she'd ever faced. It wasn't just complete, it was alien. After all, they could be anywhere in time and the universe.

"Doctor?" she said, softly at first, afraid of catching the attention of who knew what that might be lurking in the darkness. When she didn't get an answer, she raised her voice, and repeated her call several times, but the near-perfect silence remained unbroken.

She got up on her knees and her good hand, and began feeling her way around. Even though she had the distinct picture that they had tumbled down a cliff and were now lying on the ground at the foot of it, she wasn't going to risk falling into another chasm. The ground felt muddy and damp, and the knees of her jeans were soon soaked through.

She found a wall of solid rock, but her sense of direction was all gone. It might've been the cliff they'd fallen off from, or another one entirely. It came to her that she had no way of actually knowing where she was going or where she'd been before. She might be moving away from the Doctor, and she might get lost. She desperately needed light. She searched her pockets, and found her mobile phone - of course! She should've thought about that right away.

The light was tiny, but it was better than nothing. At least it would make her search slightly faster. She dug a small hole in the mud to mark where she'd started from, stood up, and continued her search in a widening circle, holding the phone in front of her as a sad excuse of a torch.

Soon, she could make out a figure sprawled on the ground, and she only needed to see the shoes to confirm his identity. It didn't take her long to ward off her worst fears: she rested her hand on his chest, and felt it rise and fall steadily. He didn't react to her touch at all, though. Neither did he respond to her shaking his shoulder and shouting at him to wake up. He clearly wasn't dying, thank heavens for that, but he wasn't all right, either, and she still hadn't got as much as a candle for light.

"Sorry about this," she told him, and plunged her hand into his coat pocket. That was the psychic paper, and a pair of glasses, and what was that, a piece of tubing? No, a stethoscope - she could use that, she decided, and picked it up. Finally, she found an object that could only be a torch.

Deciding safe was better than sorry, she pointed it away from both of them, and turned it on. It wasn't some alien device, but exactly what she'd thought it was. The bright white light was soothing, even though it revealed nothing but rocks around them.

She turned the light towards the Doctor. She needed to find out what was wrong with him, and to get there, she needed to stay calm. Try and think of him as a patient, not as a friend, let alone as the only person who might know what to do in this dark place. This was the sort of thing she'd trained for, except that she had no supplies, they were who knew where, and the Doctor wasn't a human, and - she swallowed and took a deep breath, forcing herself to concentrate. She could do this. He needed her.

She ran the beam of the torch along his body, looking for any obvious signs of trauma. His clothes were grimy and torn, just like hers, but none of the injuries she saw seemed major. Of course, that was no guarantee. The most terrible things could come with no clear signs. She tried not to think about the worst case scenarios for a human in such a situation, like life-threatening internal bleeding or paralysing spinal injuries.

She moved around him, to get a better look of his other side, and found the reason why he'd passed out. The Doctor hadn't been as lucky as Martha. The hair on the right side of his head seemed darker than the rest, matted against his scalp. Gently, she probed the area with her fingers. There was no telling whether the wound was merely superficial, or an indication of something far worse. She didn't feel any obvious fractures, but his continued unconsciousness wasn't a promising sign.

She listened to his hearts and lungs - everything all right, as far as she could tell, nothing suggesting internal injuries - and pried his eyelids open to check the pupils. Nothing worrisome there, either. Then again, she had no idea what symptoms traumatic brain injuries would cause in Time Lords.

Martha cleaned and bound the wound the best she could under the circumstances, using tissues and the Doctor's tie. He actually complained once, in a voice so low that she couldn't make up the words. For a while there she thought he might be waking up, but he just fell silent again.

Once she had finished tending to him, she sat back, leaning against a rock face. She pointed around with the torch, from the muddy floor to the rock walls surrounding them. They were in a wide passage between two cliffs disappearing into darkness above - at the bottom of the chasm they had fallen into. The wall she was leaning on was vertical, and looked like any other precipice to her. The one opposite her, the one they'd slid down, was strange, like a huge cascade of pale, molten rock, unlike anything she had ever seen. There were several tunnels and cracks in both walls, offering paths out of the main passage.

As much as she hated the idea of leaving the Doctor behind, even for a short while, and as scared as she was of this dark, unknown place, she couldn't just sit here. They needed help. It wasn't just that the Doctor was injured. They had no food or water, no warm clothes, and no idea of where in time and space they were. The TARDIS was somewhere high above them, and she doubted they could've climbed that strange, smooth rock face all the way to the top even if they had both been fine.

She did her best to memorise every possible landmark around them, took one last look at the Doctor's unmoving form, and turned her back to him. Clinging to the torch like a lifeline with her good hand, she set out to the left, along the main passage.


	2. The Crystal Chamber

Martha advanced slowly, pausing after every step or two to listen closely and to point her torch at every nook and cranny around her. Of course, the light only showed her the very beginnings of the countless tunnels leading deeper into the rock faces by her sides. She took a closer look at some of them, and they all seemed level or sloping downwards, instead of leading up and towards the TARDIS.

Every now and then, she thought she caught sight of something, the slightest glimpse of movement at the edge of her vision, or a dark shape crouched in a crack, but once she got nearer, she was proven wrong, every single time. All she could find were oddly shaped rocks. Her breathing echoed loudly in the empty passages. The place was as barren as the Moon. If there was any life here, it was very shy and stealthy.

At first, she had thought they had landed on top of a cliff on the surface of some alien world, but the more she looked around, the more convinced she became that their situation was even worse than that. The darkness was too complete - if there were any stars in the sky at all, it would never be this dark. And then there was all the rock around them. She was sure that even under her feet, beneath the mud, there was more rock. She didn't think she was walking on alien ground anymore. Instead, she was under it, deep inside the planet, in a very big cave.

Not long after she'd left the Doctor behind, the strange smooth cascade of rock to her right changed into a normal rock face. Then, the passage she was walking in began narrowing. Finally, the two walls met above her head, forming a large tunnel. It kept shrinking, until she reached a point where the roof dipped to a level so low that she would've needed to move on all fours to fit through. She didn't exactly like that idea.

Just like she had never really been afraid of the dark, she had never been seriously claustrophobic, but she had never been in a place like this before. The thought of all that rock around her, the weight of it... Besides, if something should go wrong, there would be no one around to help her. Maybe she should just turn back.

She crouched to the ground and pointed the light into the low, round tunnel. Just ten feet ahead of her, it seemed to reach a wider space, and there, she saw something glimmering.

Slightly startled, she backed away behind a bulge in one of the walls.

"Hello? Anyone there?" she called out. There was no answer. As she listened, she realised she had left the sound of dripping water behind as well. It was a silence so profound that she might've been all alone in the universe.

She thought about the Doctor, lying unconscious and injured at the bottom of the chasm, and her imagination got the better of her once again. What if there were predators in this cave, vultures, or vampire bats - what if they could smell his blood? Then again, aside from that glint in the next room, which could be anything, she still hadn't seen one sign of life, no footprints, no droppings, not even anything growing in the rocky soil. She was being paranoid, almost literally afraid of her own shadow. Besides, she hadn't walked very far yet, probably a hundred yards or so.

Martha decided she'd better take a quick look at whatever was in the next room, and then return to the Doctor.

She moved on, both knees and her good hand on the ground, holding the torch rather awkwardly with her injured hand. Her ponytail brushed against the ceiling. Even ten feet felt like a very long distance within the low, narrow tunnel. Once she was through it, she saw -

Her breath caught in her throat. She stood up and stepped closer, trying to make sense of what she was looking at.

A huge crystal tree grew from the ground, touching the ceiling and a good part of the walls, filling most of the room she was in. It looked like it was sculpted out of ice, a bluish white, glittering in the torch light, but the sculptor must've been mad, because it twisted and turned in every direction, in countless curves and spikes. It was beautiful, and completely alien.

Whatever it was, it wasn't alive, though, as far as she could see, no more than the rock walls around it. There was no trace of anything living in this room, either, nothing but crystals and rocks. The chamber around the crystalline structure was round and big, though not as high as the first passage. The beam of her torch could just reach the ceiling and the walls, which had numerous tunnels in them.

Looking at all the openings, it came to her that she hadn't marked the one through which she had entered the room. She turned around. She hadn't walked very far from the wall, but right behind her, she saw three tunnels, and they all seemed similar.

Panic bubbling up inside her again, she took a few steps closer to the tunnels, looking for any clues. Once she pointed the light at the ground, she saw a clear set of footprints marking her path. She sighed out of relief. Lucky for her that the ground was muddy. If she ever ventured into any of the side tunnels, she would need to watch out. It would be very easy to get lost in this maze.

She turned to face the strange crystal tree again. She just had to linger and gaze at it for a little longer. It was so incredible that it did away with all her anxiety. After all, how could anything malicious be lurking in the shadows of something so magnificent? The Doctor would love this.

The Doctor - oh. The thought of him was a sobering one. She'd better go back. She could always return here later, with him. The route was easy to remember, after all.

Martha returned through the low part of the tunnel into the slowly widening section, which finally opened into the huge passage at the bottom of the chasm. Somehow, the distance felt much shorter on the way back.

Both to her relief and to her dismay, she found the Doctor exactly where she'd left him. Safe, but still unconscious. Bar the close encounter with the Plasmavore when they'd first met, every time she'd found him out cold, he had always bounced back right away, ready to start running. Now, he must've been passed out for over fifteen minutes.

"Doctor?" she tried once again, kneeling next to him and pointing the torch at him. As soon as the light hit his face, his features went from impassive to a disgruntled frown.

"Aagh! Point that thing somewhere else!" the Doctor complained, rolled onto his side, and covered his eyes with his arm.

Martha quickly aimed the beam elsewhere, and crouched closer to him. "You're awake!" she exclaimed. She was so glad to see him conscious again that she really wanted to hug him, but she settled for placing a hand on his shoulder instead.

"More or less, I should think." He scrambled to a seated position, moving slowly, as if not quite sure of his balance. Once he got there, he instantly bowed his head, pressing the heels of both hands against his forehead. "Oh, my head. That's not good."

"You must've hit it pretty hard when we fell, you've been out for quite a while. I was worried for you. How bad is it? Any nausea or dizziness?" Without thinking, Martha pointed the light at his face again.

"Oi! Don't do that!" he groaned, ignoring her question, pushing the torch away with one hand and using the other to shade his eyes. "A little light sensitive here. Well, more than a little." His hand went to the side of his head, his fingers gingerly examining the injury and her handiwork. "Why am I wearing a tie around my head?"

"I had nothing else to bind it with," she said, on the defensive. She looked at him closely. There was so little light that it was impossible to tell if he was paler than usual, but obviously, the wound was bothering him, and there seemed to be other symptoms besides pain.

"Oh, all right. For a moment, I thought it was a fashion statement. It was all the rage sometime in, hm, must've been the 38th century, I think. There were several different styles, too. I never quite got the hang of it," he babbled, working on unravelling the knot as he spoke.

"Wait, you really shouldn't," she tried, but he had already undone it, and hid the muddy and bloody tie in one of his pockets.

"It's quite all right, not bleeding anymore," he assured her. He brought his hand to the wound again, and grimaced. "Already on the mend, but it still stings, and itches, too. I guess I can only blame myself. That's what you get when you go caving without a helmet."

"We're not caving!"

"We're not? What are we doing in a cave, then?"

Martha was so surprised by the question that it took her a moment to react. He didn't sound like he was joking. Was he suffering from memory loss? It wouldn't be unexpected in a human with a head injury, but somehow, it was strange coming from him, since he always knew so much about everything, and -

"Sorry, what's with the silent treatment? Did I say something rude?"

"No, no, not at all," Martha replied quickly, even more perplexed. "Besides, I was barely silent for three seconds!"

"Three seconds?" the Doctor repeated, his puzzled frown mirroring hers. "Really? It felt like at least three hundred to me. Five minutes, that is. That's odd."

"You really don't remember what happened?"

He scrunched up his face even more. "The sixties. I remember we were headed for the sixties. Funny, I don't think caving was very popular at that time. Not that it's a very common sport where you come from, either, although give it a few hundred years... Anyway, the sixties. After that..." He shook his head slowly. "Where are we? What happened?"

"I was hoping you could tell me. I have no idea. I really don't think it's the sixties, though. For some reason, we landed right next to a gaping chasm, and fell into it."

"Ah. Makes sense, I guess. Explains the lack of proper gear," the Doctor said, still sounding somewhat confused.

Carefully moving the torch to her injured hand, Martha raised her good hand, holding up three fingers. "How many?" she asked him.

He blinked hard, squinting at her hand, put on his glasses, tried again, and huffed unhappily. "More than a human hand should have. Not good." He ruffled his hair. "Big bad bump on the head, blurred vision, amnesia, light sensitivity, time sensitivity - that adds up to... Right. Of course."

"Right, of course, what? What does it mean, Doctor? Are you all right?"

"Well. Not quite. It means," he began slowly and rather dramatically, "That I have got a concussion."

"Right," Martha said, relieved that it wasn't anything more sinister than that. In a human with similar symptoms, she might've come to the same conclusion. Time sensitivity was a funny one, though. "Is a concussion the same for a Time Lord as it would be for a human? Not too serious? You're going to be all right?"

"Of course I am," the Doctor replied, a tad too quickly to Martha's liking, ignoring the rest of her questions. "So, what's wrong with your hand?"


	3. Chasm Passage

Unable to come up with anything better, the Doctor used his bloodstained and dirty tie to immobilise Martha's sprained wrist. It was somewhat challenging, since he kept having trouble focusing his eyes, but he did his best to keep that from her. To divert her attention from himself, he even went on to lecture her about how she'd been ignoring the standard first aid protocol for such injuries.

"There's that handy acronym for it, what's it, NOODLE?" he thought aloud, as he placed her bound hand to rest on the opposite shoulder. "No, RICE! Yes, that's it. Now, I can see how ice could be a problem here, but what about rest, compression and elevation?"

"I had more important things to think about," Martha replied, holding out her hand and flexing her fingers. "There's another first aid principle you may have heard of: you tend to the most serious injuries first."

"Well, this isn't all that serious," he said airily. "For a clever person, I have a very thick head."

"Are you absolutely certain about it?" she asked, her face grave, eyeing him with what must be her most clinical, doctorly expression. "In humans, symptoms that look like a concussion can sometimes be caused by something much worse."

"Trust me, Martha Jones. If I were bleeding into my brain, I would know it."

The truth was, he would more than just know it. Most likely he wouldn't have woken up at all, not with the same handsome face. For Time Lords, concussions were rare. Their complex brain was their greatest asset, and it was well protected. To get it as addled as this, he must've taken a blow that would've killed most humans. To get a brain injury even worse than this and not regenerate was unimaginable. It simply didn't happen.

"All right," Martha said, clearly unconvinced. "Still, you should take it easy. At least for humans, the only treatment for a concussion is rest."

"The same goes for me," the Doctor admitted. Of course, that wasn't the whole story, but he wasn't going to tell her that. No point making her needlessly worried. "Now, then. Let's see. We're in a cave," he began.

"A big one, by the looks of it," Martha added.

"Lots and lots of big caves in the universe, and many of them quite similar."

He looked at the ground, scooped up some of the mud with his fingers, and brought it close to his face. It didn't smell like anything specific. The thought of putting anything in his mouth wasn't exactly tempting, but he tried it, anyway. It didn't taste like anything he could recognise, either. Strange. Then again, most likely he just couldn't tell the exact chemical composition, because his senses weren't up to scratch.

"It's mud," he told Martha, lacking better information. "So, we're in a big cave, which has mud on the ground. Where exactly is the TARDIS?"

She pointed up with the torch, along one of the walls. He tilted his head to follow the light - and realised as soon as he'd done it that quick movements were a bad thing. The sudden action doubled his headache, and made the room spin. He squeezed his eyes shut. After a while, the nausea had settled enough that he could open them again and look.

The wall itself was quite a sight, a steep slope covered with what was one of the most spectacular flowstone formations he had ever seen. He thought he could spot broken parts where they had tumbled down it. He still had no memory of the fall, and he really hated that. He also hated it that his mind wasn't half as sharp as usual, but there was nothing he could do about that right now.

"All the way up there," Martha said, sounding despondent. The beam of the torch tapered away where it reached a vertical part of the rock face that wasn't covered with flowstone.

Cautiously, the Doctor lowered his head, and rubbed at his temples in a vain attempt to ease the discomfort. There was no way they could climb that rock face, not without proper gear - especially not when Martha had a sprained wrist, and he wasn't exactly in top shape himself.

"Seems we need to find another way up," he said.

"Yeah," she said. "I already took a look around, and there are lots and lots of tunnels. I'm afraid it's going to take a while to find the right one."

"Well, then, we are caving, after all! It's an adventure," he declared, doing his best to sound cheerful. "Of course, we don't have the proper equipment. It's all in the TARDIS - helmets, headlamps, overalls, boots, rope, but I think..." He searched his pockets as he spoke, and actually found one useful thing. "Ah, headlamps!" he announced, handing it over to Martha.

She took the small lamp, looking at it curiously, and unwound the twists from the head strap.

"It's not very big or bright, but better than nothing," he added.

"Is this the only one you've got?"

"Yup. That's all right, though. Wouldn't be very practical for me anyway," he gestured at the side of his head.

"Right. You should take this, then. It's yours, after all," she said, and gave him the torch. "Besides, it's not all that practical for me." She manoeuvred the strap of the headlamp around her head with some difficulty, heedful of her injured wrist, and turned on the light.

"All set? Great. Let's go," he said.

The next challenge was to get up from the floor. For once, the Doctor wasn't in a hurry to do that. The way he felt, he was almost certain that if he bolted up too quickly, he'd black out. Probably anticipating his problem, Martha offered him her hand. Slowly, concentrating on nothing but his feet and the ground, he stood up. He found himself swaying, and the room seemed to be doing the same, only not quite at the same pace or in the same direction.

There was a vertical rock face not far from him, and he decided it would make for a nice support. He took a few steps sideways and leaned on it heavily, his cheek pressed against the cool surface. It felt slightly better - at least until he got the strangest feeling that he was actually still lying on the ground, and the gravity had shifted somehow. He took deep breaths through his nose to fight back the dizziness.

"Doctor?" Martha asked, obviously worried, placing a hand on his arm.

"Yes, fine, no problem. Just need a moment. I'm getting to know the rock here," he patted the surface. "It's a very nice rock. Really rocks, this rock, it does," he told her, not entirely sure himself if his words made any sense.

After a while - he had no idea how long, since his sense of time was entirely off - he finally ventured to try standing on his own. It didn't feel impossible anymore, just uncomfortable. Of course, the worst thing was, it wasn't going to get any better anytime soon. More likely the opposite. Well, he had faced worse. Far worse, many many times. They needed to get going. The less time he spent brooding, the sooner they would get back to the TARDIS.

"Which way, then?" he asked Martha.

"There's tunnels in every direction, but I found something I think you'd like to see. That way," she gestured towards his left, waiting for him to set the pace.

He did his best to walk normally, even though his legs still felt wobbly, the passage around them was still swaying, and everything was ever so slightly blurred, both visually and temporally. Definitely a very uncomfortable experience.

Just moving took so much concentration that he couldn't really pay much attention to the surroundings. What he did catch didn't give him any clues about where they might be. The only particularly noticeable thing so far had been the exceptional flowstone cascade, which he couldn't place. They were clearly in a natural cave, by the look of it a solutional one, but that was as specific as he could get at the moment, and it really didn't narrow the possibilities down very much.

Martha lead the way along the large passage, which was getting smaller as they went. Finally, they reached a place where it became so low that walking upright wouldn't do anymore. Taking advantage of the break, the Doctor rested against the nearest wall.

"It's a little tight, you have to go through on all fours, but it's not a very long way," Martha said, motioning at the tunnel ahead of them.

"As small cave passages go, that's quite spacious, actually," he told her. She frowned at him, looking taken aback. "But, I'm sure there'll be no need for us to squeeze through any of the really tiny ones," he added.

"We'd better not. You go first." She nodded towards the opening. "It'll be more impressive that way."

"Ah, good!"

The Doctor crouched to the ground, slowly, glad to have the wall close by. He really hoped they wouldn't need to do anything more athletic than this. Then again, crawling on all fours - or on three limbs, with one hand holding the torch - was actually more comfortable than walking upright.

At the other side of the short tunnel, he found himself in a big chamber, half of which was filled by a massive crystal formation. Glimmering, ice-like, oddly shaped - he could recognise that.

Martha had emerged from the tunnel, and stood up next to him. "Beautiful, isn't it?"

The Doctor got up from the ground as well, all discomfort forgotten. "Yes, it is. Deceptively so. That is a khirindal."

"What's that? Do you know where we are?"

"Well, yes and no. It means we're in a nest of Khiandrian petromites. Can't tell if it's abandoned, or if they're just hiding from us and our lights. We're not on Khiandria, though, because Khiandrian caves are full of life, and they look entirely different. This is bad."

"Are petromites dangerous, then?"

"Not really. Not as such. They're a bit like termites, except that they eat rock - and that's not just a few little pebbles from the ground, oh no. Left to themselves, they go all the way through the bedrock. Burrow their way through asteroids, or moons, or planets. Eat them so full of tunnels that they're all hollow. You can't see it from the outside, but land on a place like that with a big heavy space ship, and the ground will collapse."

"And we're inside such a planet? All these tunnels -"

"No, not all of them. The chasm and that wide passage we followed, those were geologically formed, although some of the side passages were probably petromite tunnels. They often run into older caves as they go. But that narrow part right behind us, that's a good example - and look at this chamber here, can you see how round it is? And what the walls look like, like they've been chiselled, or gnawed? Brilliant, isn't it? Amazing what millions and billions of tiny jaws secreting a clever set of chemicals can do."

Martha was staring at him with wide eyes. "They don't eat anything else than rock, do they?"

"They're not picky, they can eat mud, and sand, and metal, and -"

"No, but I mean - us?"

"Us? Of course not! They won't touch anything organic. Well, unless you count organic remains in limestone, or -"

"Doctor, are we safe?"

"Safe? Oh, no, we're not. Far from it. Your average solutional cave has its hazards, but you don't need to constantly worry about it collapsing on top of you. Petromite nests, on the other hand... We really, really need to get out of here."


	4. The Humming Room

**Author's Note: **Thanks and hugs for all the lovely reviews, they make my day! :)

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**4. The Humming Room**

Martha was crestfallen to hear that what she'd taken for a beautiful natural wonder was actually a warning sign. She was glad she hadn't explored the tunnels further on her own. She had no idea what she would've done if she had run into a swarm of rock-eating alien termites. Most likely the same thing the two of them did after seeing the crystal tree: back away as quickly as possible.

They returned to the first passage once again, since the Doctor deemed it a safer part of the cave. He appeared much less confused now, and he was walking steadily, seemingly all right. Still, Martha didn't miss the fact that whenever they stopped, he sought for something solid to lean on, and it was obvious he hadn't told her everything. She decided to keep a very close eye on him, to make sure he wouldn't overexert himself.

"Back where we left," the Doctor noted, nodding towards the notorious cliff. "I suggest we check where the other end of this big passage goes, next. What do you think?"

"It's as good a direction as any," Martha said. She really didn't have an opinion. She didn't know a whole lot about caves on Earth, and she knew even less about alien ones - the crystal tree had made that very clear.

They kept walking past the place where they'd hit the ground, along the bottom of the chasm, into previously unexplored territory. Even though one torch and one headlamp didn't give them a whole lot of light, Martha felt much less jumpy when she wasn't all alone. She wondered whether she had only been paranoid before, or if those little glimpses of movement she had thought she'd seen at the edge of her vision had actually been petromites. Whichever the case, she saw none of them now.

Like in the other direction, both the walls soon became vertical, but the passage remained wide. While the Doctor mostly walked straight ahead, his eyes on the ground before his feet, Martha made it her task to take a look at all the openings around them. She actually found a few tunnels which sloped gently upwards. Some of them were so narrow that just the thought of going inside them made her feel uncomfortable, but none of them had the round cross section or the chiselled look that the Doctor had mentioned as signs of petromites. She pointed them out to him.

"Ah, very good," the Doctor said approvingly. "If this big passage takes us nowhere, we can try one of those."

They'd been walking for maybe ten minutes, when a third rock face appeared in front of them, dividing the passage into two narrower ones. They looked identical to Martha.

"Which one?" she asked.

"Well, this one seems closer to the right direction," the Doctor replied, and headed into the left hand passage.

There weren't many side tunnels in the passage, and after a while, it shrunk into a corridor just large enough for them to walk side by side. Then, they ran into a dead end. The tunnel widened again to form a room, about the size of Martha's flat. The far wall was different from the two others: instead of solid rock, it was a heap of boulders reaching from the floor to the ceiling, blocking their way.

Martha scanned the few recessions in the walls, only one of which looked like it might actually lead somewhere. She turned to see what the Doctor was up to, and found him sitting on the ground, the side of his head resting against the boulders. He was so still that for a moment, she wondered if he had fallen unconscious again. She was just about to ask if that was the case, when he spoke up.

"Martha? Come over here. Can you hear that?"

She crouched next to him, placing her ear close to the boulders as well. She did hear something, a low, steady humming. She had no idea what it was - it might have even been a mechanical noise of some sort, like air conditioning. She had already got so used to the deep silence in these tunnels that it was more than a bit disconcerting to hear something unknown break that quiet. It made her imagination run wild once more.

"I hear it," she told him in a whisper.

"Good," the Doctor replied, clearly not in the least daunted by the strange noise. "I was half afraid it was just my ears buzzing, that wouldn't be entirely unexpected."

"No, I can definitely hear something. Is that them? The petromites?"

The Doctor shook his head, and groaned. "Agh, I should remember not to do that. I can definitely hear a buzz now. But no, it's not them."

"Some other life form, then?"

"Can't be sure just based on the sound, but I don't think so. I think that's water. An underground river, somewhere not too far behind these boulders."

"A river," Martha repeated, trying to imagine what it would look like, and failing. The continuous rumbling sounded more like a waterfall than a river to her.

"Which is good, because if it's plain old h two o, then at least we won't die of thirst," the Doctor added practically. "If we can get to it."

"There's one tunnel in that wall which seems to go somewhere, we could try that one."

"Yes, let's..." The Doctor started getting up, his hands braced against the rocks.

"But," Martha said, placing her good hand on his shoulder to keep him down. "Now that we've stopped anyway, let me take a look at your head, all right?"

"What for? There's nothing to see. We'd better keep moving. These tunnels may be safer than some, but that doesn't mean we're out of the crystal woods."

"Just to be sure. Won't take long," she said firmly, and moved so that she could see his face. Of course, she accidentally pointed her headlamp into his eyes, sending him blinking, groaning and grimacing.

"Still light sensitive, I see," she noted.

"Will be for quite a while. Lucky coincidence that we're in a dark cave."

"And the other symptoms?"

"No worse than is to be expected," he replied vaguely, and refused to elaborate even though she asked.

She had to admit that he had been telling the truth about his head. There really was nothing to see. She combed his blood-crusted hair with her fingers, and all she could find was a patch of skin rougher than the rest. She would have wanted to check his vitals as well, but he was looking so exasperated that she decided against it. Feeling slightly less worried about his physical condition, she declared they could move on.

"Thank you, Doctor Jones," the Doctor said, in an unusually sarcastic tone, and headed for the opening she had found earlier.

The tunnel was so narrow that they had to walk in single file, and Martha didn't protest when the Doctor offered to lead the way. It narrowed even further as they went, giving her the all too vivid feeling that the walls were moving in to crush them.

The Doctor stopped and turned to look at her. "It gets a little tricky here," he commented. "I'll go and see if there's any point in both of us going through."

"Wait, what sort of tricky?" she asked, but he was moving again. As he advanced, she saw what he had meant. Ahead of her, the tunnel became so narrow that it was little more than a thin vertical crack. Somehow, standing sideways, his hands above his head, he managed to squeeze through it. It looked so small that she wondered if she could do that even if she wanted to. After all, even though he was taller, he was also, well, flatter than she was.

He disappeared from view, and she was all alone once more. This must be what a concussed Time Lord's distorted sense of time would feel like, Martha thought as she waited, growing more anxious with every passing minute - or were they seconds instead, or maybe hours?

Since there was nothing to see, she found herself paying more attention to all other senses. She could hear a soft scraping sound, which had to be him moving further into the depths, and, in the background, a low hum that was probably the sound of water they had heard earlier. It also came to her as she waited that there was a very distinct smell to this place, ancient and earthy.

She was starting to wonder if she had made a serious mistake in letting him go on alone, when the scraping began to grow louder - at first, it somehow sounded like the noise was coming from behind her, and she had to tell herself over and over again that it was an illusion, of course it was the Doctor, and it was childish and stupid to even think that it might be something else - and then, she could see the bright light of his torch shining through the narrow crack.

He stepped out, and slid down to sit on the ground, his back resting against the wall. "I found the water. Explains why the petromites have avoided this part of the cave, they don't like water," he told her, sounding out of breath, but smiling. "I'm afraid we can't reach it this way, but it's definitely there. This passage leads to a ledge overlooking the river, some thirty feet above it - it's quite a view! You should see it!"

"I think I'd better not waste our time on sight-seeing," she said quickly, relieved that there was no absolute need for her to try whether she could fit through the narrowest part or not.

They spent some time searching the room, and the passage leading to it, for other possible routes to the river, but found none. Somewhat disappointed, they returned to the point where the wide passage at the bottom of the chasm split into two, and tried the right hand passage next.

The passage went on and on, high and quite wide. It also veered to the right, a direction that was entirely unpromising, since it seemed to be leading away from both the river and the TARDIS. They had just stopped to consider whether they should turn back or keep going, when Martha heard something. Not the rumble of the river nor the dripping water from earlier, but a low mumble that she could've sworn to be a human voice. It was her turn to wonder whether it was real, or just all in her head.

"Doctor? Listen," she whispered.

He frowned. "I can't hear anything. Oh, but wait - there!" he said, his voice low but sharp. "Martha, turn off your light."

He had already switched off the torch, and was staring intently at the far end of the passage. She followed his example.

There, still quite far, but coming closer as they watched, she could see the unmistakable glow of approaching lights. She heard the sound again as well, but the distance and the echo distorted it so badly that it was impossible to tell if the voices were human, let alone what they were saying.

Martha found herself holding her breath. Even though meeting people down here would be a great help, and it was just the sort of thing they had been hoping for, her first instinct was to turn around, run away, and find a place to hide in, just in case.

The Doctor, of course, had no such misgivings. He turned on his torch again, and started walking briskly towards the people, or creatures, who or whatever they were, already shouting "Hello?" as he went. Martha had little choice but to follow him.


	5. Meeting Point

"Hello?" the Doctor called out.

"Who's there?" a sonorous voice answered him, followed by a higher-pitched, though still masculine one shouting, "Jess? Jess, is that you?"

The Doctor could see the lights stop moving as the people hesitated. Martha seemed nervous, too, staying silent, hovering just behind him. Humans, always so afraid of the unknown.

"Hello! We're friends," he tried again, still walking towards the mysterious people. He waved his hand at them, only to realise that they wouldn't see it in the dim light.

Once they got close enough, the Doctor saw there were three of them, three men, dressed in just the sort of garb one would expect in a cave: mud-covered overalls, helmets and headlights. As they caught sight of the Doctor and Martha, they froze again. He could just make out the baffled looks on their faces.

"Who are you, and what the hell are you doing in here dressed like that?" one of the men said not too politely, in a thick Southern American accent. He seemed to be the oldest of them, in his fifties, maybe.

"Caving, obviously. Same as you," the Doctor answered.

"But - how did you get in?" another man asked, his Queen's English quite the contrast to the first speaker's voice. He was considerably taller and bulkier, too.

"How long have you been here?" said the third man, who was the shortest of the three, and looked youngest as well, thirty-ish. The Doctor couldn't instantly place his dialect, but it was clearly American, like the first speaker's.

Slowly, the facts began to actually sink into his muddled mind. These weren't just any human cavers, but human cavers speaking English in recognisable American and British dialects - they were on Earth, after all!

"We sort of fell in here," Martha answered them. "And we haven't been here very long, a few hours, maybe. Now, I know this is going to sound like a really stupid question, but - where are we, and what year is it?"

"Misery Hole," the youngest man answered, sounding miserable, too.

"Carlsbad Caverns National Park, New Mexico, 1969," the oldest man elaborated.

"Ha! We weren't off course at all, then," the Doctor declared. The place, though - the place names sounded vaguely familiar, giving him that always so annoying tip-of-the-tongue feeling. "Misery Hole, Carlsbad Caverns..."

"I can't believe it!" Martha exclaimed, grabbing the Doctor's arm. "We really are on Earth. We're still on Earth!"

"Yes, yes, but -" He was missing something important here. He grabbed at his hair with both hands, but refrained from pacing around, because he didn't entirely trust the ground or his feet. "Carlsbad Caverns, New Mexico - ah! Yes! Lechuguilla Cave!"

Both Martha and the three cavers were staring at him like he had lost what was left of his mind.

"Never heard of it," the oldest of the cavers said, sounding dubious.

"It won't be called that in many years. Actually, it - I mean, this - well, maybe not this section of the cave, but the system - is only discovered in the eighties, but then, it becomes really famous for all the unique cave formations - oh!"

Oh. Oh, dear. He fell silent, gazing back at the slightly blurred faces of the four humans.

The name of the place wasn't what he had been missing. Misery Hole, Lechuguilla Cave, the name didn't matter. How come he had never realised this? He had heard of the place before, after all - he had even seen pictures. Those should've rung a bell. Apparently, he had needed to see the things in person to recognise them for what they were.

"The khirindals," he told the others.

"The khirindals," Martha repeated. "The petromites!"

"There can't possibly be petromites on Earth," the Doctor said. "Khiandria has very strict quarantine laws these days, so it's virtually impossible, but more than that, they can't be here, as in, they really, really shouldn't be here."

Could the cavers have ended up here through a rift of some sort? Could they be on another planet, after all? But no, he had seen pictures of Lechuguilla Cave, and there had been khirindals in those pictures. And since Lechuguilla Cave was on Earth, it followed logically that, as impossible as it was, there really were, or at least had been, petromites on Earth.

If this was an active nest, the workers would eventually dig their tunnels under towns and cities, and there would be accidents, cave-ins, collapsed buildings, all sorts of disasters. The Doctor hadn't actually seen any petromites yet, so it was possible that the nest was abandoned. He would have find out. Of course, it would be dangerous, going into those tunnels - not to mention he had no idea how he could actually stop the petromites if he needed to - if only he didn't have this murderous headache. He hung his head, his crossed hands resting on the back of it.

"I'm sorry, could we perhaps start from the beginning here?" the British caver spoke up, interrupting the Doctor's thoughts. "I have absolutely no idea what you have been talking about for the last minute or so. I'm Joseph Stratton. I don't think I caught your names yet?"

"Martha."

"The Doctor."

"Of what?" the oldest caver asked.

"A little bit of everything," the Doctor answered him. "And you are?"

"Geology."

"What? That's your name? Geology?" the Doctor repeated.

The man laughed, quite a sound thanks to his deep voice, and shook his head. "Of course not. I'm a doctor of geology. The name's Grant. So, what's yours?"

"Like I said. The Doctor."

"That really is your name?"

"Yup."

The Doctor could notice Martha was fighting back a chuckle, and the youngest caver seemed to be doing about the same.

"They say you have to be a little crazy to do stuff like this, and I guess they're right," the young man said. "I'm Brian, by the way."

"Brian, Grant, Joseph," the Doctor repeated. "Pleased to meet you. Very pleased, actually, considering the circumstances. Although, if you're stuck here as well, that means we're all stuck here, possibly with petromites, in which case, it's actually not very pleasant for any of us. So, I guess I should say, I'd rather not have met you here, but in some entirely different circumstances, but since we're all here anyway, well -"

Everyone was staring at him again. Was he making any sense at all, or just babbling in gibberish? It wasn't impossible, after all. He couldn't really be sure, could he? "Sorry. Concussion. If I stop making sense, please let me know."

"You're always saying things that don't make sense to most people," Martha noted.

"I am?" the Doctor said, daunted. "Oh. Well. Anyway, where was I? The circumstances. Yes. So -"

"We're stuck," Brian said, before the Doctor had managed to put together anything coherent. "You mentioned that it's a bad thing if we're stuck here, and we are, and yeah, it is. We've been stuck for over a day, we've already lost Jess, we've run out of food, our lights aren't going to last much longer, and there's little hope of us ever getting out of here."

"Actually, there may be more hope for you now that you've met us. You see, we've got a way out," Martha said. "If we can find our way back to it. We can help each other."

"But the way back is sealed shut, blocked by several collapsed passages," Joseph said.

"Our way is a little different," Martha assured them.

Originally, the Doctor's plan of action had been simple: get to the TARDIS as quickly as possible, then get out of here. Once safely out of the cave, they could've taken a look at the planet to see whether the petromites were a problem or not. Now, they needed the answer to that question more than ever, but since the nest was likely to be quite small, it wouldn't be possible to find out from outside the cave. Still, heading for the TARDIS first probably wouldn't be a bad idea.

"Have you got a map?" the Doctor asked. "A survey?"

"Of course," Grant said. He set his tackle bag on the ground, and after some fishing about, produced a large rolled-up plastic pocket, which he spread on the ground, revealing their map of the cave. They all sat down around it.

The Doctor put on his glasses and squinted at the drawing, trying to force all the squiggly lines into some semblance of order. The map seemed to cover the entire area he and Martha had seen so far, and a lot more.

"We're sitting right here at the moment." Grant pointed at a spot. "We were just on our way back from exploring this section," he gestured at the continuation of the passage they were in. It ended in a chamber, which seemed to have a pool in it. "Beautiful columns and draperies, breathtaking, but a little annoying, too, since I've absolutely no idea how those formations came to be."

"Sulphuric acid dissolution, chemolithoautotrophic bacteria, and petromites," the Doctor said.

"Sulphuric acid dissolution?" Grant repeated. "There's a new one. Sounds interesting, you'll need to tell me more about it. Anyway, that's either a dead end or a sump. This is where we originally came from," he went on, tapping at a corner of the map where the lines ended. He started tracing a path with his finger to show their course. "Like Joe said, it's blocked, right there," he tapped at another spot. The line lead to the chamber with the khirindal. They had come here through the petromite tunnels. No wonder they had got trapped.

"And this is where we need to go," the Doctor said, pointing at the top of the cliff where the TARDIS was.

"That's your way out? A cliff top? You want to jump off a ledge?" Brian asked. "Not that I don't understand the feeling, but..."

"No, no, of course not!" Martha said. "It's not the ledge that's important, it's what lies next to it. Please believe us. It's our best hope for getting out of here."

"It's as good an idea as any that we have," Joseph remarked. "After all, we have none, except for exploring these tunnels for as long as we live, on the thin chance of finding an alternative exit."

"True enough. Okay. We've been up there, and there's several routes we could pick. The fastest and most obvious one would be to climb up, but it's a bit challenging, and since you don't seem to have any gear..." Grant mused, his hands still on the map, sizing up the Doctor and Martha.

"No gear, and we're a bit beaten and bewildered, too," the Doctor admitted. "Any alternatives that don't include climbing or rappelling?"

"There's always that one," Brian pointed at one of the many tunnels fanning out from the passage at the bottom of the chasm. This one met with a long passage marked with waves. "We go through to the river, and follow it upstream."

"Oh, I'd rather not go through that again," Joseph complained.

"Sorry, Joe, but he's right, that's probably the easiest way for them," Grant agreed. "It's a little uncomfortable, and not exactly the shortest route, but it's very straightforward, and doesn't require using rope techniques."

"To the river it is, then," the Doctor agreed. "But before we go, say, you wouldn't happen to have any medical supplies? Ace bandages, maybe?"

"Should have some in the first aid kit," Brian told him, and pulled the said kit out of his bag. "Who's hurt? I have first aid training."

"And we're both doctors. Well, sort of," the Doctor said. "Martha, your wrist?"

The young man helpfully offered to bandage Martha's hand, and the Doctor didn't complain. Brian probably did a better job of it than the Doctor would've done. Once he was finished, Martha raised her eyebrows at the Doctor. "What about you?"

"Me? I'm good," he lied. He wasn't, of course, but there was nothing in the cavers' supplies that could help him. "Which way to the beach?"

The adrenaline boost of running first into a khirindal and then into people was fading away all too fast, and the Doctor was again starting to fully register the utterly jumbled state he was in, mind and body alike. As they got up, no matter how slowly he tried to move, his vision greyed out for a few seconds. Not that he could tell if they really were seconds, but it couldn't have been much longer than that, since no one seemed to notice. As he stumbled forwards in a haze that refused to clear up, he wondered how much longer he could hang on.

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**Author's Note/Disclaimer:** If you want to see where the inspiration for the khirindal came from, go to wikipedia and look up Lechuguilla Cave, it's right there. :) Obviously, I haven't actually been to the place, and I'm not writing this fic based on a map or anything, so the geography of the cave in my story is completely made up. I have been to other caves, though. I like caves. Yay.


	6. Stratton's Squeeze

They were on Earth.

Martha still had a hard time actually believing that fact, even though they were now walking along the cave passage with three men from the sixties. She was glad they had met them. Not that she didn't trust the Doctor's abilities and wide knowledge of all of time and space, but these were people who had clearly spent a lot of time in places just like this, and already knew this particular cave quite well.

"So, what do you do? Are you both geologists as well?" Martha asked Brian and Joseph as they walked.

"I'm more of a well-informed amateur in that field," Joseph replied. "Photography is my actual line of work. Of course, I abandoned all my equipment once we realised we're stuck here. No sense in lugging all that extra weight around, when no one is ever going to see the pictures anyway."

"I'm not a geologist at all. I'm a teacher, actually," Brian said. "Elementary school."

"What's a school teacher doing in a cave, then?" Martha asked.

"I'm mostly here for the adventure and the excitement, and..." He sighed. "Well, I wouldn't be here if not for Jess."

"Oh, you mentioned him earlier - what happened to him?" Considering Brian's tone and the fact that he had said they'd lost Jess, maybe she shouldn't have asked that, but she couldn't help being curious. "Of course, I understand if you don't want to talk about it," she added quickly.

"It's okay, I think you'd better hear our story since we're in this mess together now. And it's not him, it's her. Jessica Solis. You may have heard of her, she's one of the top speleologists around here," he said, paused, and sighed again. "Was, I should say, I guess. She's the one who found the entrance to this cave, and she was always the one to go through the most challenging obstacles first, but then... There was this boulder choke, and it seemed all right, we all agreed on that, no loose boulders, just very tight - and she went through first - but it wasn't all right. It shifted. Collapsed on top of her. We did our best, but we couldn't reach her, and she wouldn't answer our calls -"

"There was nothing we could do," Joseph added, his voice wavering slightly as well. "We had no choice but to leave her. She's gone."

"That's horrible! I'm so sorry," Martha said.

"I guess we'll all be joining her soon enough. Maybe she was lucky. At least it was quick for her," Brian said gloomily.

"We won't," Martha reassured him. "We're going to get out of here, all of us. The Doctor and I, we've been in situations far worse than this. There's always a way out."

Martha kept expecting for the Doctor to speak up, but he was being strangely quiet. She had thought he was feeling better. Maybe she'd been wrong. He was walking ahead of her, next to Grant, who was leading the way. He seemed to be staring at his toes instead of looking around, and that alone was a clear sign he wasn't back to normal yet.

They walked back to the crossroads, followed the familiar wide passage for a few minutes, and then Grant stopped. "This is it," he said, nodding towards one of the walls. "Our shortcut to the river."

At first, Martha didn't even understand what he was gesturing at. When she did - she felt her mouth go dry and her palms turn sweaty at the very idea. There was an opening in the wall, but it was so low that she would never ever have considered it a possible passage.

"They insist on calling it Stratton's Squeeze, in my dishonour," Joseph said unhappily. "But you are both much smaller than I, so it should be easy enough for you."

"I really don't know about that," Martha said. "I've never done anything like this before."

"Don't worry, it's really simple, and it's not that tight all the way through," Grant said, doing absolutely nothing to reassure her.

"What exactly are we facing, then?" the Doctor asked. Even he wasn't sounding too enthusiastic.

"Just crawling, with some squeezes, all in a nice straight line. Maybe fifty yards or so," Grant explained. "That's the uncomfortable part. After that, some wading and a few traverses in the river, and a walk in a wide, easy tunnel. Let's see - I can go first and guide you, Doctor. Martha, you come after him, then Brian, so you can help both her and Joe. That sound all right to you?"

"Fine, I'll come last so I won't slow you down too much," Joseph muttered.

"I think I'll be taking it slow, too," Martha said.

The entrance of Stratton's Squeeze was a little larger than she'd thought at first. She could actually fit through it on her knees and elbows. After the first few feet, the ceiling rose a little. She kept going. She tried not to think about where she was, and did her best to keep her head clear and just concentrate on moving. She could do this.

She could see the Doctor not far ahead of her, and hear Brian just behind her, pushing his tackle bag in front of him. The tunnel was so narrow that simply turning around would be a challenge. Then, the Doctor stopped moving.

"Gets a little squeezy here," he announced, his voice sounding muffled in the tight space. "So, here we go."

She followed him through the tight section, and it wasn't all that bad, although Martha could see why Joseph had complained about it. He was quite a bit bigger than her, after all. She did have to crawl, pressed flat against the ground, and her clothes got completely covered in mud, but that was unavoidable. If it wasn't any worse than this, she'd survive. She couldn't imagine why anyone would want to do something like this voluntarily, though.

After the first squeeze, they had it easy for a while, but then, the Doctor stopped again, and proceeded really slowly. Soon, all Martha could see were the soles of his trainers, sticking out of a very narrow horizontal crack, like the rock had swallowed him alive - it even looked like he was trying to fight against the stony maw, his toes shuffling against the ground as he squiggled his way through.

She stared at his shoes, holding her breath. Oh, God, how could she do this? And what if she couldn't? What if she got stuck? This was far worse than the first squeeze, and worse than the narrow vertical crack the Doctor had gone through earlier. He seemed to have no trouble with this one, either. She would have to do it, too. There was no turning back now.

The Doctor's shoes disappeared from view. "All right, Martha, I'm through," he called out.

She braced herself, and started crawling.

"Turn your head sideways, and keep at least one hand extended ahead of you all the time," Brian advised from behind her. "And remember, you can't get stuck, not really. If you were able to get there, it's always possible to get out, too."

She somehow managed to get her head and her good hand through the tightest part. She could see to the slightly wider space beyond, where the Doctor was sitting in an awkward-looking position, his back against one wall and his trainers against the other, his pulled-up knees almost touching his chin. He gave her an encouraging smile.

She tried to keep going, but she wasn't getting anywhere. Her shoulders were at the tightest part now, and it really was tight, it was so tight that she couldn't breathe - she thought about petromite tunnels that could collapse any minute - surely this wasn't one of those? And the lost caver, Jess, who had been buried under rocks, probably suffocated, crushed, just like this -

"Martha?" the Doctor called out, sounding worried. "Martha, it's all right. Relax. You're safe."

She swallowed, and tried to calm down, but it felt completely ridiculous - how was she supposed to relax when she was stuck between who knew how many tons of rock - when there wasn't even enough room to take a deep breath?

"You can fit through, if the Doctor and I could," she heard Grant say.

The Doctor crouched in front of her and gave her his hand. "Come on, I'll help. We can do this."

He pulled, and she kicked with her feet and tried to wriggle her way forwards as best she could, and slowly, all too slowly, she was moving, an inch, then another, and she almost got stuck and panicked again when it was her hips at the tightest part, but somehow, she managed it, and finally, finally she was through. She pulled up her knees and wrapped her arms tightly around them.

"All right, Brian, the coast is clear," Grant announced.

The Doctor somehow managed to worm his arm around Martha's shoulders despite the lack of room. "Are you all right?" he asked.

She nodded, not trusting her voice yet. She must've got a dozen new bruises, but she was still so panicked and shaky that she didn't even feel the dull pain of her wrist.

"That was the worst of it, the narrowest part of this whole trip. You did good," Grant said from behind the Doctor.

The Doctor reached over Martha to pull Brian's bag through the squeeze. Next came his helmet, and then, Brian himself emerged through the tight section.

"Quite a thrill, that one," he said, grinning. Then, he saw the look on Martha's face, and turned more serious. "We're not far from the river now, and the rest of the journey is much easier than what we've just gone through."

"All right," Martha managed to say. "I'm ready, let's move on."

They kept going, and the tunnel grew slightly bigger, high enough that she could've walked in a low crouch instead of crawling, but she stayed on her hands and knees. She wasn't entirely sure her feet would carry her.

She wanted nothing more than to get out of this horribly cramped space, and that was what kept her going through one more squeeze, not quite as tight as the previous one, but no less scary for that. Even the tunnels where there was no risk of getting stuck felt much too tight now. She had to keep reminding herself that there were chambers as huge as houses in this place, and if she just kept going a little longer, they would soon reach one of those.

Finally, the walls disappeared from around her, turning into darkness instead, and she could breathe freely again. They weren't in a room, but in a high passage, on a wide riverbank made up of rocks and boulders. The roar of running water was very loud here. The river itself was much smaller than she would've expected, more like a rapidly flowing stream.

The Doctor was sitting on the ground right next to the opening, staring into the distance. Immensely relieved that they had both made it safely through that terrible tunnel, Martha made her way to him, and wrapped her arms around him.

"Now, this sort of squeezes aren't too bad," he told her over the noise.

She just chuckled tiredly, and hugged him a little tighter.

After a while, she realised that his forehead was resting on her shoulder, and he was leaning on her really heavily.

"Doctor?"

His head snapped up, he sat up straight, and blinked at her blearily, raising his hand to rub at his eyes. "Oh, I'm sorry! Do we need to go?"

"We're not in a hurry," she replied. Had he just nodded off there? She didn't think Time Lords did that. Had he blacked out, then? "Doctor, if you need to rest -"

"No, actually, we are," he interrupted her, got up, and headed towards the river.


	7. The River

"Okay. A few general guidelines before we go on," Grant said, standing on a stepping stone in the river. "First of all, don't even imagine you can keep your feet dry. Not going to happen. We'll be wading most of the way. It's no more than knee-deep, except for a couple of deeper pools, which we'll need to traverse. Secondly, watch very carefully where you put your feet. There are countless small potholes and ridges, and..."

The Doctor found it immensely difficult to concentrate on what Grant was saying, especially with the constant roaring of the water drowning half the words. Not that it mattered. This wasn't his first encounter with an underground river. He already knew the basics.

He realised his eyelids were sliding shut again, his head drooping, when Grant raised his voice to a cheerful holler. "Off we go, then! Remember, follow exactly in my footsteps, and watch your feet."

The Doctor stepped from the stony bank into the cold water. It wasn't deep at all, only up to his ankles, but the current was strong, the water foaming white here and there. He stared at his feet, or what he could see of them. How exactly was he supposed to watch them, when the swirling water was enough to make his head swim? It was all so blurred that he couldn't tell apart any details. He looked up instead, at Grant. Copying the geologist's moves seemed like the easier option.

They began wading upstream, keeping the same order as before: Grant first, the Doctor after him, then Martha, Brian and Joseph. Like the Doctor had expected, it turned out to be much more difficult for him than crawling in the small tunnel. He wasn't claustrophobic, and he felt more comfortable lying down, so the tunnel had been all right, as physically draining as it had been. The river, on the other hand, was a real struggle.

He was fighting both the current, with all the hidden hazards under its surface, and the sleepiness that was threatening to overwhelm him. What made it especially difficult to ward off was that it wasn't uncomfortable, not like the nausea or the headache. It would be a blessing to close his eyes and drift off - but he couldn't! Not yet.

He turned his attention to the path ahead of him just in time to stop before he collided with Grant, who had turned to face him. They waited until Martha and the two other cavers had gathered around, too.

"There's a big pothole ahead of us, several yards deep, but luckily, it's not very wide, so we can cross it easily enough. There's plenty of good holds, just keep one hand and one foot on both walls, and take it nice and slow. It's not difficult. I'll go first and show you how to do it."

The Doctor saw Martha tense up next to him. This was, again, something completely new to her. Hopefully, it wouldn't be quite as scary as the tight tunnel. At least there was plenty of space around them. And plenty of water under them. He wasn't entirely sure whether that was good or bad.

They took a few more steps forwards, and then Grant planted a boot on a ledge in each wall, well above the surface of the river, grabbed at suitably shaped holds with his hands, and covered the next ten feet or so moving like that. It really didn't look too difficult. Grant stood at the other side of the pothole, facing the others, and beckoned with his hand.

It was the Doctor's turn next. He needed to put away his torch so he could use both hands, but the others' headlamps gave him enough light. Finding holds wasn't hard, especially since he could do it by feeling around, without needing to look. The walls were wet and slippery, but there was little risk of slipping accidentally, when he had all four limbs on good holds.

He was almost over the deep part, when a particularly bad wave of dizziness washed over him - oh, this really wasn't a good time - he tried to shake it off, but of course, shaking his head only made things worse - he wasn't even entirely sure which way was down, anymore.

Suddenly, the rumble of the river disappeared, like someone had just switched off the sound. The lights, too, because for a blink, he saw nothing but darkness.

The next thing he knew, he was underwater, a strong current pulling him deeper into the seemingly bottomless pit. Underwater - he could handle underwater. Longer than a human, anyway. Long enough. The water was ice-cold, and his clothes were a heavy weight dragging him down. Down, yes, that was down. The pull of gravity. That was where he didn't want to go. The other direction would be good.

Wide awake now, he kicked furiously with his feet and paddled with his hands, trying to create at least a little lift against the current. He didn't seem to be moving much. He reached up with one hand, seeking the surface.

A strong hand grabbed his, and began tugging. He clutched at it with both his hands, and more hands seized his, drawing him up. His head broke the surface, and there were hands all around, helping him to shallower waters. He landed on the riverbed on his hands and knees, coughing and spluttering and shivering. Someone was trying to wrap a blanket around his shoulders, but he pushed them away.

Someone - probably a different someone - helped him stand up, and then he could see Martha right in front of him, the painfully bright headlamp all too close to his eyes, her hands squeezing his arms tightly. "Are you all right?" she asked.

He needed to cough a little more to find his voice again. Finally, he was able to answer her. "Fine, fine! It was refreshing, actually!"

Martha stepped back from him. "If you just wanted to take a bath, you could've warned us first!" she shouted. For a moment, she looked like she was ready to punch him, but the angry look faded quickly, giving way to open worry. "What happened?"

"I'll explain later," he told her. He wasn't going to start discussing his health with her when they were in the middle of the river.

All three cavers were standing close to him and Martha. Apparently, Grant had traversed the pit again to return to the others. They were all soaked, too. Not quite as wet as the Doctor, but very nearly so, their sleeves drenched all the way to their shoulders.

"What now?" Brian asked.

"Maybe we should turn back," Joseph suggested.

"And then what?" Martha said. "Go through the Squeeze again?"

There were no banks in the river where they stood. It flowed in a high, narrow tunnel. Nowhere dry to go anywhere near them. Not that the Doctor needed to. He wasn't cold. Instead, the shock and the drop in temperature had been like a sharp slap in the face which had woken him up - he mind felt clearer than it had in a good while. The silver lining of this particularly wet rain cloud. The humans would start feeling chilled, though, if they weren't already, unless they started moving soon.

"I'm all right!" the Doctor shouted, louder than before, so that everyone would hear him. "We should keep going."

"But there's another big pothole ahead," Grant told him. "And we're not even past the first one yet. You really think you're up to it? Do you realise how incredibly lucky you are that we managed to drag you up from there?"

The Doctor decided that trying to explain to the cavers about his superior physiology wouldn't be worth the trouble. "Yes, to both," he simply answered. "And thank you for rescuing me, but really, that was just - I just slipped. It won't happen again."

"We could rig it," Brian said. "Use a rope as an extra support, or even as a belay."

"True, we could make do with what gear we've got," Grant agreed. "But then again -"

As much as the Doctor valued conversation, right now, it was slowing things down too much. He didn't feel anywhere near to normal, but he wasn't too dizzy, either, and most importantly, he wasn't sleepy anymore. He could take advantage of that. If they moved quickly, they might be able to reach the TARDIS before he started dozing off again.

"Standing here and speculating isn't going to help anyone. Come on, let's go!" he declared.

He turned to face the pothole again, and grabbed at the holds. Before anyone had time to try and stop him, he was halfway over it, and then at the other side, standing in the river again, out of breath, his hearts trying to outrace each other, but otherwise no worse for wear.

Grant followed the Doctor over, and seized his shirtfront, pinning him against the wall. "I don't know who you are or where you come from, Doc, but if we're doing this together, we make our decisions together! This is a dangerous environment, there's no room for showing off!" he rumbled. Someone who wasn't over nine hundred years old might have found the furious tone combined with the booming voice quite scary.

The Doctor looked deep into his eyes, unwavering. "I know, and I'm sorry, I really am. I'm all for democracy and co-operation, in more ways than you'll ever know, but this is a bit of an emergency."

"It had better be!" Grant growled, and let go of the Doctor's shirt.

The Doctor sagged against the wall, still trying to get his wind back.

Grant went on to motion at the others that they should cross as well. Martha did it next. The Doctor could tell she was nervous about it. No doubt seeing him take a swim hadn't made it appear any less scary. She stood on the first footholds, clutching the rock tightly with her good hand, and shook her head.

"I don't know what to do next!" she shouted.

"It's all right, stay there, I'll guide you," Grant said. He crossed the pothole once again, to stand on footholds in front of Martha. "Now, see that ridge, there, right in front of your right foot? Step on it. There, just like that, yes, that's fine. Then, your left foot..."

Having a sprained wrist obviously hampered Martha's progress considerably, but moving slowly and cautiously, with Grant telling her where to place her hands and feet, she was able to make it. Brian and Joseph followed her with sure, practised moves.

Brian walked up to the Doctor. "Don't mind Grant," he said close to his ear. "He can be a bit intimidating. Some of his students call him Granite, you know. Because that's what he's like if you get on the wrong side of him."

"Granite - that's funny. And I don't mind. He did have a point, after all."

They continued on their way. The second pothole followed not long after the first one, and to everyone's relief, they were all able to cross it without any major trouble. Then, it was back to just wading again, staring at the whirling current.

The dizziness was returning with a vengeance, growing worse with every step. Soon, the Doctor had no choice but to use the walls for support again. The sleepiness hadn't come back, but he wasn't sure if that one good thing about the incident outweighed all the bad ones. It had sapped most of what little strength he'd had left. His feet felt almost too heavy to lift, his legs shaky, and the weight of his soaked clothes wasn't helping at all. He kept having trouble catching his breath, and his hearts were still acting up. All in all, maybe he would've rather been sleepy. He desperately needed to rest. Soon, he told himself. They couldn't be far from the TARDIS now.

He had no idea how long they had been walking. The distance felt much longer than he would've expected. Eventually, they reached a section where the wall to their left became lower. There were several big ledges in it, almost like large steps, offering them a fairly easy path up from the water.

Grant went first, and offered his hand to the Doctor. A little clambering, then a few strides on level ground, and he'd made it through a crack into a sheltered chamber, where the roar of the river was much lower. Even leaning on a wall, he had to muster every ounce of determination he had left to keep himself upright.

"How much longer until we're there?" he asked Grant.

"About two hundred yards of walking. Like you probably noticed, we needed to go past the point where we're headed to be able to get out of the river. Now, we'll be doubling back through that dry passage," Grant explained, motioning at a tunnel leading to their left, which sloped steeply upwards. His patronising tone made it clear that he was still cross about the Doctor's actions in the river. "After that, it'll be all up to you. I've got to say, I'm very curious to see what that mystery exit of yours is like."


	8. Hope Passage

Martha's jeans were soaked halfway up her thighs, her shoes were full of water, and she was convinced she would never, ever want to see another cave after they got out of this one. In a way, she could understand why people came to these places - after all, she did something similar herself. Travelling with the Doctor was dangerous, but she loved the adventure and all the incredible things they saw. Still, that horribly tight tunnel and the river with its countless hazards had been so trying that she wouldn't want to face anything like those again, not if she could avoid it.

Brian and Joseph helped her up a series of high steps, onto solid ground, where they went through a narrow opening into a completely dry chamber. Grant was already there, sitting on the floor. He had taken off his boots, and was wringing out his socks.

The Doctor - Martha almost missed him at first, because he had turned off his torch. He was leaning on a wall, looking tired and queasy, hunched forwards, with his arms crossed and his palms pressed against his sides. If she hadn't known it was his head that was injured, she might have suspected something else entirely. She hadn't had the time nor the chance to check him out after that plunge he had taken. Had something changed? Had he sustained new injuries?

"Doctor?" she called out.

"Hmm, how long have I been here?" he muttered, sounding slightly confused. His face lit up when he saw her. "Oh, Martha! Hello."

Without even bothering to ask him if he was all right, she placed her fingers on his neck to check his pulse. Instead of the alien but familiar double beat, she found something even stranger: a rapid, varying pattern of double and single beats. She frowned at him.

"You know me, always a little offbeat," he joked. "It's nothing serious. We should keep going."

"I'm not having any of that anymore. You might be in a hurry, but I'm not," she told him firmly, and dug the stethoscope out of her pocket.

"Hey, that's mine, isn't it? How did you get it?"

"Doesn't matter." She brandished the instrument at him as if it was something really sharp. "Just hold still and keep quiet."

He huffed and pouted, but did as she asked. She unbuttoned his sopping wet jacket and pressed the bell against first one side of his chest, then the other. The constant low hum of the river made it impossible to listen to any fine details, but she could hear that his left heart was beating almost three times as fast as his right. No wonder he had been looking queasy - she couldn't imagine what that would feel like.

"Seriously, Martha, it's not serious," he said once more. "Just uncomfortable."

She shook her head at him. "I'm done with you dodging all my questions, mister! What's really wrong with you? I may not be a doctor yet, but I know concussions don't cause arrhythmias."

"Not in humans. Well, not in Time Lords, either, not directly," he said. She thought he was actually sounding apologetic. "This is more of a chain reaction, cascade effect sort of thing. But it's still a concussion, nothing more, nothing less. You know what a concussion is, right?"

"Of course I do. It's a mild form of traumatic brain injury that happens when -"

"Yes, yes, but I'm talking about the details here. The important thing is, when you hit your head hard enough, bang!" He clapped his hands together to imitate the impact. "It muddles up the normal processes of your brain, metabolism, neurotransmission, a dozen important little things."

Martha nodded. The fine mechanics of a concussion weren't all that well understood yet, so the Doctor probably knew a lot more about the subject than any human doctor did. "It can take days or even weeks for everything to return back to normal, right?" she asked.

"If you're human. Slow and inconvenient. I could do it a lot faster. Twenty hours, I think, that would do the trick. Twenty hours in a healing coma, that is. Which is something I can't have, not here and now, not until we're safely back in the TARDIS."

"And before that..."

"Yup." The Doctor made a very unhappy face. "I'm not going to get any better. I'll only get worse. Which is why we need to stop wasting time and get going." He stood up straight, but kept one hand on the wall for support.

"But that still doesn't explain the rest of your symptoms!" Martha insisted.

"It does, actually. Chain reaction, like I said. Complicated physiological response. This," he tapped his chest, "And the sleepiness, and the blackouts, like that one in the river, and a number of other things - that's my body trying to convince my mind that I need to go to sleep. Well, not as much convince as command, at this point. Actually, we're not even on speaking terms anymore. It's down to fighting, tooth and nail, and there's really only one possible outcome. But, I'm fairly certain we can reach the TARDIS before I keel over, so all's well. Allons-y!"

He started shuffling towards the one large tunnel leading out of the room. He looked so unsteady on his feet that Martha placed herself by his side, and draped his arm over her shoulders to help him. The three cavers followed them, keeping quiet, probably listening in curiously. Martha didn't pay them any attention.

"Why didn't you tell me any of this earlier?" she hissed at the Doctor.

"What good would it have done? There's nothing you could've done to help me. You would've just been overly worried for nothing."

"And you think I haven't been worried when I've watched you grow worse by the minute, without any idea why?"

"I was rather hoping you wouldn't notice," the Doctor said meekly. "Of course, I also assumed we would get to the TARDIS before it got this bad."

They had barely taken five steps, and he was already winded. It was no wonder, since the floor of the passage they were walking in was very steep. It felt strenuous to Martha as well. They were leaving a set of wet footprints on the ground as they went.

"For someone as old as you, you can be incredibly daft," she told him.

"Senile and concussed. Not the best of combinations."

She ignored his wisecrack. There really was nothing amusing about the situation. "When we do reach the TARDIS, what's going to happen?"

"Well, obviously, I'm going to sleep, twenty hours straight. You won't be able to wake me up, but that's nothing to worry about. It's a bit like hibernation. Very low body temperature and barely perceptible vital signs. And then I'll wake up good as new, and we can start worrying about the petromites."

She was really looking forward to seeing the police box again. Maybe she'd take a nap, too, once they got there, especially now that she knew what was going on with him. As annoyed as she was about how he'd kept her in the dark, she was relieved that it was nothing too serious after all, and that he would be getting better as soon as he got his badly needed rest.

"You were going to tell me all this sooner or later, weren't you?" she asked him dubiously. She could just imagine how anxious she would've been if he had never told her a thing - if he had just suddenly collapsed, seemingly lifeless, without her knowing about the healing coma.

"Of course I was."

"And when are you going to tell us a thing or two, then?" Grant's voice joined the conversation.

All Martha's attention had been on the Doctor, so the geologist had been able to walk up to them without her even noticing. He was standing right in front of them now. The tunnel was wide enough for three or four people to walk side by side, but the Doctor was leaning so heavily on Martha and the wall next to him that Grant effectively blocked their path.

"Because I'd really like to know what sort of lunatics I've been guiding around this cave," Grant went on. "For starters, what's a TARDIS? Since that's what we're looking for, right?"

Martha sighed. Of all the times to have this confrontation - couldn't they have waited just a few more minutes? She knew Grant was angry at the Doctor for taking matters in his own hands in the river. She hadn't been too happy about that, either, but now that she knew the Doctor's situation, she could easily understand why he had been in such a hurry.

"You'll see for yourself once we get there," she told Grant, and tried to take a step forward, but he just crossed his arms, a stern look on his face.

"But what is it, then?" Joseph asked. "What can be so strange that you can't even answer that question?"

"It's a big blue box. It travels in time and space," the Doctor told them, with barely half of his usual enthusiasm.

"No, but seriously," Joseph said.

"He's being serious. It's a spaceship and a time machine. I know that sounds crazy, but can we at least keep moving?" Martha pleaded. "He hasn't got much longer."

Grant held his ground. "And why's that, then? That talk about hibernation, what was that all about? Who are you, really?"

"I'm just a medical student," she replied. "Nothing mysterious about me, honestly. The Doctor..."

"The Doctor is about to become a big heavy extra weight you'll need to carry around," the Doctor declared. "If we don't move along."

"Grant, come on! We're almost there," Brian spoke up. Martha could've hugged him for standing up for them. "Shouldn't we at least go and see for ourselves, like she said? There's no harm in that."

"We can't really even know that for sure, can we?" Grant said, but nevertheless, looking reluctant, he stepped out of the way, allowing them to continue their ascent. "So, you have a spaceship. What does that make you, Doc? The man on the Moon?" he asked as they began walking again.

"That, and a few other places," the Doctor said. It felt to Martha that he was leaning on her more and more heavily with each step. "The Moon is nice, though, isn't it, Martha?"

"Really pretty," she agreed.

"Lunatics, just like you said," the Doctor announced triumphantly.

Grant shook his head. "I can't believe this."

"They did appear from out of nowhere into a previously unknown cave system that's supposed to be inaccessible at the moment," Joseph said, aiming his words at Grant.

"And the Doctor obviously isn't in perfect health, you can't deny that," Brian added. "Besides, why would they be making this up?"

"I've no idea. I guess we're about to find out," Grant said.

They walked on in a charged silence. Martha couldn't really blame the cavers for not believing her and the Doctor. She doubted she'd have believed herself either, had she been one of them. Luckily, it didn't matter - she was sure they'd be convinced as soon as they saw the inside of the TARDIS.

The last yards felt like they were moving in slow motion, but finally, the steep passage opened into a wide area with a level floor.

"Here's your cliff top now," Grant stated. "So, where's your spaceship?"

They moved ahead, the Doctor still leaning on Martha, and looked around, keeping an eye out for the edge of the chasm. The strange thing was, the room they were in wasn't all that big. Their lights could reach most of it. She would've thought they'd be able to see the TARDIS already.

After a few more steps, the Doctor sank to his knees. "But - no! No, no, this isn't possible!" he breathed, sounding desperate.

Following his gaze, Martha could spot the ledge that had broken under their weight - but the TARDIS was nowhere in sight.


	9. TARDIS Square

For the second time in not too many hours, the Doctor felt like the ground was giving way under his feet. Of course, this time it was purely metaphoric, but it left him every bit as confused and hurt. The thought that they'd soon reach the TARDIS had been what had kept him going those last exhausting yards. Now they were here, but she wasn't. It was too awful to be true.

The Doctor's first thought was that they were in the wrong place after all, because the TARDIS couldn't be gone. She simply couldn't, it made no sense - but that chasm in front of them looked awfully familiar, and he could remember hanging on to that rugged edge for his dear life. He could even see a square-shaped imprint on the muddy floor where she had been. It wasn't the wrong place.

He couldn't think, he couldn't breathe, his vision was growing dim at the edges - he was at the end of his rope, and he had no idea what to do next. No longer having the energy to stay on his knees, he slumped to sit on the ground.

Martha knelt next to him, placing her hand on his back. "You could rest here, couldn't you? You could just stop fighting it. We could look for the TARDIS later, when you're feeling better."

"No, no, don't even say that! I can't, and you mustn't let me," he said urgently, because he wanted nothing more than to let go, but he knew he shouldn't. Her telling him to do it in a friendly, soothing voice wasn't helping at all. "Not without knowing what's happened to her. No. Twenty hours later it could already be too late."

"Then we need to figure out what's happened," Martha stated matter-of-factly.

"Yeah," the Doctor agreed, but it was easier said than done. His head felt like it was about to split in half. He grabbed it with both hands. Maybe he could keep it together if he pressed hard enough. He guessed he must be looking every bit as sick as he felt, because Grant still hadn't made one snide remark.

"We landed here, stepped out, and - oh, dear! I don't think I locked the door," Martha said, sounding mortified. "But we're on Earth, in the sixties, in a cave with a collapsed entrance. How could there be anyone here who'd know what the TARDIS is, let alone how to fly it? For all we know, there's no one here but us, and - the petromites! They couldn't have..."

"The petromites, right," he repeated, trying very hard to think. "The TARDIS smells and feels and tastes just like wood, so they wouldn't eat her. But I guess they could've taken her."

"How intelligent are they, then?"

"They have a hive mind of sorts. A typical nest is about as smart as a dog. An ordinary dog from Earth, I mean, of course."

"But you think they could've stolen the TARDIS?"

"Oh, no, no, not stolen as in flown away. Just taken her. Moved her elsewhere. But why would they want to do that? None of this makes any sense!"

"Their being here in the first place doesn't make any sense, either, right?"

"It doesn't." He hung his head, closing his eyes. His ears were ringing. They were missing a piece of the puzzle, he was sure of that, but he couldn't even begin to imagine what it might be.

"Anyway, if the petromites took the TARDIS, how can we find it?" Martha asked.

He looked up again. "Martha Jones, that is a very good question," he told her. How glad he was that she was there and being her bright and brilliant self, when he was having such a hard time trying to be even half as clever as usual.

If the petromites had taken the TARDIS, finding her might not be all that difficult. He couldn't give up yet. His mind claiming the upper hand over his body once more, he crouched very close to the ground, down on his elbows, and crawled to the spot where the TARDIS had been. There were some small rocks on the ground nearby.

"Turn off your lights, everyone," he said. "Or point them away from me. I need darkness here."

Martha turned off her headlamp. Apparently, some of the cavers didn't do that, because there was still a little light, but he hadn't got the strength to start arguing with them. It would have to do. He adjusted his 33rd century torch to Khiandrian light, soft and greenish.

He lifted one of the rocks, then another one - no luck there. He found another pile of rocks, turned some of them around, and there! He was in luck, after all! He could only see it as a tiny glowing blur, but what else could it be?

"Hello, there," he whispered, put his torch on the ground, cupped his hands, and managed to pick the beastie up between them. He showed it to Martha.

"What's that? Is that..."

"A petromite, yes." It was standing still on his palm, apparently frozen in fear.

"It looks like a glowing ant," she commented. "I thought they'd be bigger."

"Like termites, like I said. Now, if we're really lucky, this little one here just might lead us to where his friends have taken the TARDIS."

"Hold on - you're saying that these tiny things may have actually been able to move it?"

"These tiny things are really strong, and there are lots and lots of them. Now, the thing is, we'll need to go into their nest. It's going to be dangerous. Those tunnels aren't just prone to collapse from outside reasons, the petromites can make them cave in as a defence against intruders, which we are obviously going to be. So, a very dangerous business," he explained, addressing both Martha and the cavers. He realised he was speaking really quickly, probably sounding both breathless and frenzied, but at least he could still speak. Better say it all while he could. "I'm not asking anyone to come with me. Actually, it'd probably be better if you didn't. You can stay here and I'll come and pick you up once I've found the TARDIS. It'll take at least twenty hours, though."

"You can't seriously expect me to let you go there all alone!" Martha exclaimed.

"Well, not really, I don't," he admitted. "Not you. But the rest of you."

The cavers stepped closer, their lights pointed at him. The Doctor closed his hands protectively around the petromite. The bright lights could both frighten and hurt the creature.

"I have no idea what you've been talking about, but of course I'm coming," Brian said. "I believe you. I believe you really can get us out of here."

"I don't know about that, but your plan is still better than ours, which is non-existent," Joseph said. "And I'm curious about this all. I'm coming with you as well."

Grant shook his head, arms crossed, looking as grim and granitic as ever. "That doesn't leave me much choice, does it? Follow you, or wait here on my own? Let's go."

"Well. All right," the Doctor nodded slowly. He hadn't expected they'd all want to come. It complicated things. The more there were of them, the bigger the risks. "Once we leave this room and enter the nest, we must keep as quiet as possible, all the time, and move slowly. Minimise the risk that they'll consider us threatening. You'll also need to turn off your lights. That's all we can have," he nodded towards his torch. "One of you should take it, actually.

Grant picked it up from the ground, frowning at it disbelievingly. "This, for all the five of us? How're we supposed to see where to step?"

"Crawl, not step. We'll feel our way around. Should be easy enough. Petromite tunnels are smooth and level. Now, then. Lights off," he said.

Brian had already switched his lamp off earlier, and Joseph and Grant finally did the same. The Doctor gave them a moment to get used to the Khiandrian lighting they'd be travelling in, and then he set the petromite on the ground in front of him.

It wasn't moving. He was afraid he'd accidentally hurt it, and he was starting to get desperate, until he realised that he might just be misinterpreting the passage of time once again, taking seconds for minutes. When the little glowy smudge began to creep away from him, he almost didn't notice it.

"Here we go! Follow me," he told the others. "And remember, keep quiet. Don't even whisper, not until I say it's all right."

He went after the petromite on his knees and elbows, his nose almost touching the ground. Martha followed right by his side, and the three cavers behind them, carrying the pale green light.

By the time they reached the opening of a tunnel at one edge of the room, the energy the Doctor had managed to find once he'd realised what they needed to do was almost entirely spent. Having hope helped a little, but there was no getting around the fact that he was working beyond his limits.

His world shrank to nothing but the feel of the rock under him and the sight of the little spark in front of him, leading their way towards the TARDIS. The ground was cool and smooth, and he was glad to be so close to it, because he was so dizzy that he didn't think he'd be able to stand anymore. His head was pounding, matching his madly skipping hearts.

There was no telling how big this nest was. They might still have a long way ahead of them. It also came to him that the petromite might be taking them anywhere. No reason for it to be going to the TARDIS, really, was there? But it was much too late to think about that. Maybe they would at least learn something useful.

The petromite kept going, moving almost too fast for him now. They were passing crossroads and turning around corners, and he knew they'd have little chance of finding their way back on their own. After a while, the Doctor began to see more glowing spots, other petromites, just a few of them, here and there on the floor by his hands - or were they just lights swimming in front of his eyes? The ringing in his ears was so loud now that he couldn't even hear the sound of the five of them crawling in the tunnel. The lights were growing dim.

He only realised he was lying on the ground with his eyes closed when Martha shook his shoulder. He tried to get up on his hands and knees again, but he couldn't. The room was spinning so fast it was like he had jumped out of the TARDIS in mid-flight in the Time Vortex. He landed heavily on his side, barely able to suppress a groan. He rested his cheek on the ground and squinted forwards. He could just make out the glint that was their petromite.

He rolled onto his stomach and started crawling, afraid that he'd lose sight of their little guide. He had to keep going, he had to hold on - but it was so hard. Too hard. He didn't even have the strength to hold his head up anymore. No matter how hard he tried, he couldn't help it. His eyes slid shut, and this time, he didn't open them again.


	10. The Nest

Martha very nearly cried out when she realised the Doctor had fallen unconscious again. It was incredibly difficult to keep quiet when what she really wanted to do was to shout at him to wake up on top of her voice. She reached for his shoulder, but this time, she couldn't rouse him, no matter how hard she shook him.

The three cavers had gathered close to her and the Doctor. Grant pointed the soft green light at him, and Brian helped her turn him over, so that he was lying on his back. She did a quick check of his vital signs: breathing fast and laboured, pulse rapid and irregular, and his skin felt warm to the touch. Hadn't he said that everything would slow down and his body temperature would drop when he went to sleep? Of course, that would probably take some time.

Brian raised his eyebrows, nodding towards the Doctor. Martha shrugged and shook her head. It seemed likely to her that he had simply reached his limit, and wouldn't be waking up for another twenty hours. Grant spread his hands, his expression clearly saying "what the hell are we going to do now?"

Martha looked away from the Doctor, towards where they'd been headed. The petromite they'd been following was almost out of sight, if she was even looking at the correct one. There were several glowing ants in the tunnel, and more than one of them were moving in the same direction. If they wanted to keep following theirs, they didn't have much time.

They still needed to find the TARDIS, and the Doctor had thought this was their best shot. She motioned at the cavers that they should take up carrying him, and went after the petromite. Apparently, the cavers weren't about to question her decision, because she could hear them start moving behind her.

She looked over her shoulder. The round tunnel they were in wasn't quite as claustrophobic as Stratton's Squeeze had been, but it was so low that there was no room to stand, and so narrow that two people could only just fit in it side by side. Carrying an unconscious person wouldn't be an easy task. Brian had grabbed hold of the Doctor's upper body, and Joseph seemed to be supporting his legs. Grant came last, holding the torch. Martha was glad the cavers had come along. Had she been here alone with the Doctor, she would be having a very difficult time now.

As they crawled on, she could see more and more petromites around them. Soon, there were so many that she had to be very careful where she put her elbows and knees. She could only hope that the cavers wouldn't accidentally squash any as they dragged the Doctor along, because she was pretty sure that would count as a threatening action.

Avoiding the alien insects took so much concentration that it was well nigh impossible to keep track of which one of them she was following. On the other hand, the majority of them seemed to be going in the same direction. That seemed like a good choice to her, so she switched from following one petromite to following their trail.

Because they didn't have all that much light, and Martha was staring at the ground in front of her, she was taken completely by surprise when they emerged in a larger space. She raised her head, and saw the greenish light from behind her reflected from a large crystal formation, similar to the one she'd seen before, but of a slightly different shape. Another khirindal, smaller than the first one, in a slightly smaller room. There were lots and lots of petromites around it, not just on the floor, but on the ceiling and the walls as well. She didn't think they were eating the rock, though. They all seemed to be going somewhere or the other.

She still couldn't see the TARDIS anywhere, and it dawned on her that they were hopelessly lost. She had no way of telling apart their petromite from the countless others, and they'd been in such a hurry that as far as she knew, none of them had been doing anything to keep track of where they were going. There were about ten tunnels leading out of the chamber. Where to go next?

The three cavers emerged from the opening behind her, and set the Doctor on the ground. She turned towards him, to do another cursory check. If anything, he felt warmer than before, feverish. The Doctor had hardly explained everything to her in great detail, but she didn't think this was the way he was supposed to be. Even though she didn't expect him to react, she tried shaking him once again.

He drew a deep breath, and let out a groan. "Did I drift off again?" he mumbled, slurring his words like he was too tired to articulate properly. Now, Martha could guess why he'd seemed agitated even when unconscious. He had been straining to stay awake all along.

"Ssh," she hissed, keeping an eye on the petromites around them. A few had stopped at the sounds breaking the silence, but most seemed to be going about as if nothing had happened. The last time the Doctor and Martha had seen a khirindal, they had spoken in normal voices. Maybe that was all right. She wished she could know for sure.

He opened his eyes a crack. "Martha? What's going on?"

"You've messed up again, that's what," Grant said in a low voice.

Martha glared at him, and whispered a sharp "Shut up!"

"It's all right, you can speak here," a female voice spoke up, the tone casual and friendly.

The Doctor bolted up next to Martha, grunted, gasped, and started to slump backwards. She quickly placed herself behind his back to help him stay upright. He sagged against her, but kept his head up, looking for the source of the unexpected, unfamiliar voice.

"J - Jess? Is that you?" Brian murmured. "But - you -"

"Brian, darling, I'm so sorry," the woman answered, and stepped into plain sight from behind the khirindal.

Jess was dressed in overalls even muddier than the other cavers', but she had no helmet or headlamp, and there was something very odd about her. She was short and wiry, and even in the soft green light of their torch, she looked paler than everyone else, almost gleaming white. Her hair was close-cropped and very light, and Martha thought her eyes looked strangely colourless, too.

"But - Jess! What - what's happened to you? What's wrong with you?" Brian stammered.

"Brian..." She sighed and shook her head. "Nothing's wrong. This is what I really look like. The way you know me, that was just props and make-up. I'm really sorry. I never meant for you to see me like this."

"Oh! You're a -" The Doctor made a rather disconcerting choking sound, cleared his throat, and tried again. "A Khiandrian!"

"Yes, I am," Jess admitted. "But what are you? You sound and smell different from the others. Different from anyone I've ever met, actually."

"I'm one of a kind, I am," he said. Since he was propped against Martha, she could practically feel the effort it took for him to speak and to stay conscious, each shaky breath a new struggle.

The cavers were staring at Jess, completely dumbstruck, and speaking simultaneously - "What do you mean?" - "Jess, are you nuts?" - "Why?" - "Who are you?" - "How did you survive?" - on and on, questions that weren't really helping, as important and interesting as it all was.

Martha raised her voice to make herself heard. "If you're a Khiandrian - the petromites are from Khiandria, too, right? Did you bring them here?"

"Not on purpose," Jess answered tersely. "They stowed away."

"That's why you have the quarantine laws," the Doctor rasped.

"Well, yes, that's right," Jess said slowly. "The thing is, I didn't go through quarantine. I was sure I didn't have any extra passengers with me, and I was in a hurry. It wasn't exactly my ship."

"You stole a ship?" Martha asked. "Did you take the TARDIS, too?"

"The TARDIS? You mean that wooden box? No, I didn't."

"So, you don't have it, then," Martha said, with a sinking feeling.

"No, no, I mean, yes, I have it, but I didn't take it. They did," she gestured at the petromites around them. "The brainless little twerps... You see, I came here to look for my ship, because - because I thought it was time for me to move on, but it wasn't here anymore. They had eaten it. Can you imagine that? Stupid mites. Of course, I was mad at them, and they were ashamed, and they wanted to make up for their mistake. So, they found this unknown thing which had materialised from out of nowhere, and they thought I might like it, so they brought it to me."

That sounded so silly, and sort-of cute, that Martha almost felt like chuckling. As smart as a dog, the Doctor had said about the petromites. As loyal, too, apparently. The Doctor didn't comment on Jess's explanation, and Martha noticed his head was bowed, his chin resting against his chest. She shifted, and squeezed his arm, but he seemed to have passed out once again - unconscious, but still fighting, judging from the way he was breathing.

"How far is it?" Martha asked Jess. "Can you take us there?"

"Not far at all, and of course, I'll do that. I hope it's not my fault he's that sick. I'm really sorry about this all. Never meant to cause anyone any trouble, but I completely messed things up," Jess said.

"But - but - I still don't understand!" Brian cried out.

"Can't you talk about it later?" Martha pleaded.

"Yes, and it's going to be a very long conversation," Jess said. "Now, please, let me help."

She walked over to them, scooped up the Doctor, and slung him over her shoulder as if he weighed nothing at all. Martha could hear the cavers gasp in amazement behind her. It was quite a sight, since the Doctor was so much taller than Jess, but Martha didn't find it all that baffling herself. Jess was an alien, after all, and Martha had seen aliens who could do far stranger things.

The Khiandrian lead them to one of the many openings in the room, probably the largest one, high enough that they could walk upright. Where she went, the petromites scurried away, giving her a clear path. There was clearly some kind of a special relationship between the alien termites and the woman.

Like Jess had promised, it wasn't a long walk. Less than ten minutes later, they found themselves in another room with a khirindal, the largest one Martha had seen so far. Standing at the foot of the huge mass of crystals, which looked like an entire frozen forest, was the familiar angular shape of the TARDIS.

"In there?" Jess asked, nodding towards the police box. "You'll need to unlock the doors."

"Yeah, okay," Martha breathed, so overwhelmingly relieved that she could barely speak.

"We'll wait here, then," Joseph said, making the obvious assumption that the TARDIS was exactly the size it looked.

"No, no, you should come with us, there's plenty of room," Martha said, as she turned the key in the lock. Apparently, the door had sealed itself when she had slammed it closed.

She held the doors open, letting the caving team in. Even Jess hesitated at the doorstep, shading her eyes with her hand, peering at the brightly lit console room with a look of disbelief on her face. The Doctor was stirring on her shoulder, as if he could sense where they were - and maybe he could. She set him down on the grating.

Martha crouched over him, and brushed back his muddy and damp hair. "Doctor? We made it. We're in the TARDIS."

He opened his eyes and squinted at her, one eyebrow raised. "We really are, aren't we?"

"Yes. It's all right, you can rest now."

"Thank you, Martha Jones." He closed his eyes again, and took a very deep breath. For the first time since Martha had found him unconscious at the bottom of the chasm, his face relaxed completely. She was slightly startled when she didn't hear another breath follow the first one, but he had told her to expect that.

"Is he..." Brian whispered.

Jess tilted her head and frowned, as if listening closely. "Still alive, for now," she declared. "Hanging by a really fine thread, by the sound of him."

"He's in a very deep sleep, but he's going to be all right," Martha said, doing her best to convince herself. She didn't exactly like the idea that she'd have to wait twenty hours before she could be absolutely sure about that.


	11. The Throne Room

Martha decided that lying on the grating for twenty hours wouldn't be good for the Doctor, and asked Jess to carry him to a bed instead. On the way, she showed the cavers where they could find the bathroom, the wardrobe and the kitchen. The three men stayed behind as the women took the Doctor to Martha's bedroom - she still didn't know where his was, if he even had one.

Once they'd reached the room, Martha had little choice but to ask for Jess's help in taking off the Doctor's soaked clothes, since her injured wrist would've made doing that on her own well nigh impossible. Even though undressing patients was hardly new to Martha, she found the situation extremely awkward. Jess, on the other hand, was very businesslike, and soon, they had stripped him to his underwear and covered him with blankets.

After Jess had left, Martha went on to examine the Doctor properly. She was glad he had warned her about what this coma state was like, because if she hadn't known better, she would've taken him for dead. His skin was ice-cold, and she couldn't feel his pulse at all. Listening very carefully with the stethoscope, she could just pick up the faintest whisper of his breathing and the startlingly slow beats of his hearts - she only counted six per minute. If Jess had actually been able to catch those from a few feet away, her hearing must be incredible, and it was no wonder she had thought he was dying.

After several hours of sitting with him and mopping the grime off his face with a wet cloth, Martha headed out of the room to take a quick shower, and changed into clean clothes. Unlike she had expected, she wasn't feeling sleepy at all herself. She was much too anxious, not to mention curious about Jess and the petromites and everything else. With a pang of guilt, she realised she had no idea what the Khiandrian and the cavers had been up to while she had watched over the Doctor.

She found Grant and Joseph in the kitchen, making tea. It was actually the first time she saw them in good lighting and without their helmets. Grant's hair was thick and steel grey, Joseph was almost completely bald. Their haphazard clothing made them look even less familiar - Grant had jeans and a flamboyant Hawaii shirt, Joseph's khaki suit brought to mind a tourist on his way to a safari.

"How is the Doctor?" Joseph asked, sounding genuinely concerned.

"Resting," Martha replied. "Where's Jess? And Brian?"

"Outside, I think. They wanted some privacy," Joseph said.

"And no wonder they did, after everything that's happened," Grant added. "I'm still thinking I must be hallucinating. We're lost in the cave and dying from starvation, and I'm imagining things. Spaceships and people from other planets - and Jess being one of them..." He shook his head.

"Did you know her well, then?" Martha asked.

"I taught her a few courses, and went on several caving trips with her. She's really good at this stuff. A promising young lady, I used to think. Now, I don't even have any idea how old she really is. Other than that, I didn't know her all that well," Grant answered. "She and Brian, on the other hand, they were really close. Everyone was expecting them to get engaged soon."

"Oh, dear," Martha said. "I think I'd better go and see if I can find them."

She didn't have to look far. Brian was in the console room, sitting on the floor near the door, his back against the wall and his knees pulled up. He was still wearing his wet and muddy overalls. His helmet rested on the floor next to him, and his sandy hair was plastered against his head. She sat down next to him, not sure what to say.

They sat in silence for a few minutes. Then, he spoke up in a soft, desolate voice. "It's all my fault. She did what she did because of me. She had run away from her home world as a teenager, she was hiding on Earth, and then, she met me, and we fell in love. And she thought we were becoming too close. Because she was sure I'd never understand if she told me who she really is, and she couldn't go on living a lie. So, she was going to leave. Make it look like she had died in a caving accident, return to her spaceship, and fly away."

Even though Martha had heard how Jess had addressed Brian, and she remembered how broken Brian had sounded when he'd told her about Jess's supposed death, his story took her by surprise. She wasn't sure what she'd expected Jess's motivations to be, but surely not just love.

"That doesn't make any of this your fault," Martha assured him. "You couldn't have known."

"Maybe not." He shrugged. "I have no idea what to do now."

"If she's still the same person you fell in love with -"

"That's just it! How can I know if she is?" Brian interrupted her. "She had long black hair and dark eyes - she used to say her father was Spanish. She's been lying to everyone all this time, pretending to be someone she's not. I don't know what to think about all this - I mean, she's not even human!"

"That doesn't have to change anything."

"Oh, right." Brian looked at her, his brow furrowed. "You and the Doctor... He's not human, either, is he?"

Martha sighed. "It's not like you think. But yes, he's not human, and he's no less loveable for that."

Brian didn't comment on that, just stared into the distance for a while, and asked, "What's going to happen next?"

"We've got seventeen hours to wait before the Doctor wakes up," Martha answered. "After that, we'll be leaving. Where to, I don't know. It's up to you, I guess."

"She still wants to leave Earth. She said as much."

"Maybe you should talk to her about it."

"I'm not sure she wants to talk to me anymore. I'm not sure I want to talk to her."

"I'll talk to her, then," Martha decided, not because she wanted to set herself up as a mediator in this intergalactic love story, but because she wanted to hear Jess's side of things, to find out if she had been sincere with him. "Where is she?"

"I don't know. Somewhere out there," Brian answered, gesturing at the door.

"I'll find her. Come on, the others are having tea."

She took him to the other cavers, and picked up the Doctor's torch from them. She paid the Doctor a quick visit, too - no change - and stepped out of the TARDIS, back amongst the rock, the crystals and the petromites.

Luckily, Jess was almost as easy to find as Brian had been, crouched in the shadows of the khirindal right behind the TARDIS. "Hi," she greeted, still facing away. She could probably recognise Martha without seeing her. "I never caught your name."

"Martha. What's yours? Your real name, I mean."

"Jess. That's what I've always been called," she answered, pronouncing the "j" in a strange, explosive way Martha didn't think she'd be able to imitate. "Not Jessica, though. Martha, meet the primary queen of this nest." She turned around and held up her hand. On her palm sat the largest petromite Martha had seen so far, at least six inches long, and that wasn't counting the antennae.

"Um, hello," Martha said tentatively. "Can she understand us?"

"Aliens like you, not at all. Khiandrians like me, just a few simple words and phrases, but they're quite good at picking up our moods. They're upset now, because of me and Brian. I've been doing my best to soothe them, but they've got a hard time trying to understand why I'm so miserable, if everything's all right. Yes, it's all right, don't worry," she told the queen, and set her on the ground next to the khirindal. She quickly disappeared into the crystal formation.

"It's all so easy for them," Jess said wistfully. "The workers dig and build, the kings travel around and breed, the queens sit in their khirindals and lead, and that's all there is to it. At least as long as we don't make things more complicated for them."

"So, the khirindals are like their castles?"

"Castles, or thrones. The prime queen lives in the largest and most elaborate one, leads the entire nest, and answers to the caretakers."

"You mean - they're domesticated?"

"Back home, of course they are. It's better for both us and them. Otherwise, they'd eat half the planet. We help them by keeping water and big predators away from their nests." She sighed. "I never thought I'd say this, but I miss home. Coming here and seeing their tunnels made me feel it more strongly than I'd have thought possible."

"We could take you there, as soon as the Doctor wakes up."

"It's not quite so simple," Jess said, and stood up, crossing her arms. "I was young and angry and fed up with the whole place, always cooped up in our caves, with all the strict rules regarding travel to other solar systems. I ignored all of those when I took my mother's ship and left. I've been here for twenty years. I don't know what kind of a welcome I'd get if I went back."

"If you really miss the place, I think you should go anyway - but you should talk to Brian before you make that decision."

"I guess," Jess said, walking slowly along the edge of the khirindal. "I don't think he wants to talk to me, though. He's right to be mad at me."

Martha walked after her. "He didn't seem that mad at you. Just sad and confused."

"Oh. Of course. That's what he's always like, always so kind to everyone. Poor Brian - I've really been horrible to him. I was so sure things could never work out between us. I thought I was doing the right thing, running away, even though it tore me apart."

"You should apologise to him, then," Martha said.

"I will," Jess answered. "But I'll need some time on my own first. If you don't mind."

Martha stopped in her tracks. "Of course. I'm sorry, I didn't mean to intrude."

"No, it's all right. I'm glad you came. Thanks. I hope your friend will be better soon."

Jess kept walking until she passed from sight, into one of the tunnels. Although the petromites made way where she went, there seemed to be a good amount of them following in her wake - like they were worried, and wanted to keep her company.

Though Martha had had doubts about Jess's sincerity earlier, those were all gone now. She returned to the TARDIS, and went straight to the Doctor. He was exactly the same as when she'd left his side. Not that she had been expecting anything different. She checked the time. About sixteen hours left.

She joined the cavers in the kitchen again. Brian had showered and changed, too. Somehow, he looked older than before, his hair combed back, wearing a blue dress shirt and black trousers. Martha spent a few hours with them, listening to their stories about adventures they'd had on other caving trips, and elsewhere - Grant had done a fair bit of mountaineering, and Joseph had travelled a lot. Brian was subdued, only saying a word every now or then, and the others were carefully avoiding any serious subjects.

Everyone fell silent when Jess appeared in the doorway. "Brian, we should talk," she said, leaning on the frame, her arms crossed.

"We already did," Brian answered, his voice flat.

"Yes, but there's more to say. Please."

"Okay."

He stood up and followed her out of the room. Not long after they had left, the older cavers announced they'd like to rest. Martha managed to find beds for them, and returned to the Doctor's bedside. Thirteen hours left.

She was starting to feel tired herself. She lay down next to him on the wide bed, and closed her eyes. With nothing to keep her attention away from her wrist, she realised how horribly sore it was. No wonder, after all the stress she'd put on it during their trip through the cave. She had to get up again to take some painkillers.

Even when the ache had settled to a tolerable level, she still had serious trouble catching sleep. Every time she was about to get there, she jolted awake, afraid that something was wrong with him, and couldn't relax until she'd made sure he was still alive. Finally, after going through that cycle half a dozen times, she actually drifted off.

She woke up to a soft knock at the door. She must've been even more tired than she'd thought, because a quick look at the clock revealed she had slept for over ten hours straight. Two hours left. The knock was repeated, louder this time.

"Yes," she said, and sat up.

The door opened a crack and Jess peeked in. "Is he any better?"

Martha glanced at the Doctor. He looked exactly the same as before, every freckle and line standing out on his pale face. "Hard to say," she answered. "We can't really know until he wakes up."

The door opened a little more, and Martha could see Brian standing right next to Jess. "Care for some company as you wait?" he asked.

"Sure," Martha said. "Please, come in."

The two cavers entered the room and sat down on the floor. Everything about their body language spoke plainly that there were no hard feelings between them anymore. Martha was glad to see that. They stuck to small talk and didn't say a thing about their situation, or whether they had made any decisions concerning their future, but Martha was sure she'd hear about it soon enough.

A little later, Joseph and Grant joined their company as well. Grant seemed to have got over his grudge against the Doctor, since he appeared every bit as concerned about him as everyone else.

As the twenty hour mark approached, Martha kept anxiously looking for the slightest sign of change in the Doctor's state. She couldn't see any.

Finally, the moment she'd been waiting for arrived - and nothing happened. He slept on.

Her worry rising to a whole new level, Martha forced herself to wait a little longer, in case the timing wasn't all that exact, or his system simply needed a while to sort itself out. Even ten minutes past the mark, nothing had changed. His skin was still unnaturally cold, his breathing and heart rates were still absurdly slow, and he still seemed completely lifeless.

From what he had said, she had got the idea that he was supposed to come out of it on his own. That didn't seem to be happening. She decided she'd better take matters into her own hands, and tried shaking him, and shouting at him, and pinching his arm. He didn't even twitch.

She looked up at the four cavers. "I think something's wrong," she said, her voice coming through all shaky.

* * *

**Author's Note: **Sorry, another cliffhanger! I can promise you it's the last one, though - this was the second-last chapter. :)


	12. The City of Lights

It took the Doctor exactly four seconds and fifty-three hundredths of a second to go from a pleasant, fuzzy, semi-wakeful state to wide awake, his mind sharp and clear. To his annoyance, he found he still couldn't remember falling into the chasm, but he guessed that was something that was never coming back. Of course, the memories of the last minutes - or hours? - before he'd went to sleep were a complete blur, too. There had been petromites, and crawling - and a Khiandrian, who had accidentally brought the petromites here.

He sat up and took in the surroundings. He was in a bed, in a room in the TARDIS - probably Martha's, judging from the items he could see, the clothes and the books. The randomly scattered medical supplies were a little surprising, though. Martha herself was standing right next to the bed, together with the three human cavers and the Khiandrian.

"Good morning! So, let's see. What're we going to do about the petromites?" he asked them.

No one answered. Instead, they gaped at him as if he had just sprouted antennae and turned glowy - or... He couldn't possibly have! He had been sick, but surely not that sick. He didn't feel any different. The teeth were familiar. He ran his hand through his hair, and it was as big as ever. So much for that explanation. He was definitely still in the same body, and feeling absolutely brilliant.

"What's wrong? What did I miss?" He was about to leap up from the bed, but stopped when he realised he wasn't wearing much of anything. "And what happened to my clothes?"

The stunned silence lasted a few more seconds. Then, Martha stepped forwards, sat down on the bed, and grabbed him in a very tight hug. He raised his eyebrows at the cavers, perplexed. They just smiled at him.

She let go of him, but kept a hand on his shoulder, holding him at an arm's length. "You've been in the coma for twenty-four hours. You said twenty!" she told him in an accusing tone. "Do you have any idea how worried we've been? We tried everything we could think of, from smelling salts to tea, and you just wouldn't wake up!"

"Whoops. Well. I must've been sicker than I thought, then. It's hardly surprising I underestimated the time, considering the condition I was in."

"You could've warned me it might take longer!"

"Sorry. Didn't think about that. I did have some serious problems in the thinking department, after all. But really, the important thing is, they're all gone now. I'm great!" He shifted on the bed, eager to get up and start solving the problems at hand.

"Not so fast," she told him, and pressed him down by the shoulders. "Not before I'm convinced about that, too."

She placed a hand on his forehead, then picked the stethoscope from around her neck and took her time listening to his chest and back. A lot more time than he would've thought necessary, really, but she completely ignored his restless squirming. When she was finally done with that, she sat back and held up four fingers. "How many?"

"The square root of sixteen, and, as it happens, the number of Khiandria's moons, if you count the artificial ones."

"That's right," Jess confirmed. "Two moons, two stations."

"No dizziness, no nausea, I love bright lights, I know Time inside and out, and I'm as clever as ever," the Doctor listed. "Now, if you don't mind, I'll go and make myself decent. Meet you in the console room in six minutes." Moving as quickly as he could, so that Martha wouldn't be able to stop him, he draped a blanket around himself and scuttled out of the room.

Five minutes and fifty-seven seconds later he dashed into the console room, dressed in his blue suit. "So! The petromites!" he began. "They're really not supposed to be here. Of course, they're much less of a problem now that we've got a Khiandrian present. All we need is for you to ask them to come in, so we can take them elsewhere."

"But there's at least two million of them in this nest!" Jess exclaimed.

"That's hardly a problem," the Doctor said, motioning at all the space around them. "As long as you can convince them not to touch anything. The TARDIS is alive, but not all the materials are organic. I don't know what they'll make of that."

"They're a little wild since they've been on their own for years, but I think I'll manage," Jess promised.

"Only one big question left, then," Martha said. "Where are we going to take them?"

"Any uninhabited world should do," the Doctor answered.

"We could take them home," Jess suggested. "Back to Khiandria. Because that's where we want to go anyway." She exchanged meaningful glances with Brian. There seemed to be a lot going on between those two.

"Both of you?" Martha asked.

"Yes. Even if it means never seeing Earth again," Brian said firmly. "She already knows my home. I want to get to know hers."

"All right, we can do that. So, that's where," the Doctor said. "Then, there's when."

"When, what?" Jess asked.

"The TARDIS travels in time as well as space," Martha explained.

"I had forgotten you'd said that!" Brian said. He took Jess's hand between his, looking excited. "Do you realise what that means, Jess? We could go there so many years after you left that no one would remember what you did - we could even go there before you left!"

"Hold on a second - what exactly has she done?" the Doctor asked. He wasn't planning on assisting criminals, after all.

"You've got quite a bit of catching up to do after all that time you spent sleeping," Joseph remarked. He was right, of course. The Doctor knew next to nothing about Jess, but since everyone was treating her like a friend, he had had no reason to assume she was anything else.

"I stole my mother's space ship. I'm not proud of it - I was young and irresponsible. I just wanted to get away from home, to see the world. I'm not a thief," Jess declared.

"All right," the Doctor said slowly. "I do know that feeling."

"And I'm not a coward," she went on. "I'm prepared to take the blame for what I did. I say we go to Khiandria on this very day, not some other time."

"Good choice," the Doctor said, and walked over to the console to make some adjustments.

"You may look different, but you really are the same Jess we've always known, aren't you?" Grant said fondly.

"I've never been anyone but myself, no matter what I've looked like," Jess said.

The Doctor flicked a switch, but instead of Khiandrian-style lights, he ended up putting them in pitch darkness. "Oops, sorry!" he shouted, fumbled for the switch, found it, tried again, and this time, he actually got the gentle green glow he had been aiming for. "There, that's better! Mood light! Not moonlight, though!"

"And you're every bit as loony without the concussion," Grant added. Oddly enough, his tone wasn't scornful, but good-natured and friendly.

The Doctor grinned at him. "Oh, yes!"

"You can take me and Joe home after we've dropped these young people off on that alien world, right?" Grant asked.

"Of course. Martha and I might even come along. Earth, the Sixties - that's where we were headed in the first place. But before that, next stop, the glimmering caves of Khiandria!"

They propped the TARDIS's doors wide open, and Jess went outside to fetch the queen. Once she returned, she was followed by a wide, continuous stream of petromites. The Doctor couldn't help feeling a little apprehensive for his TARDIS, but the creatures seemed to be behaving well, just scurrying in and settling on the ceiling and the walls and under the grating.

"You're quite good at this, aren't you?" he remarked to Jess, who was sitting in the middle of the room, the queen resting on her lap.

"Ah, well, my grandmother was the caretaker of a large nest," she said, sounding pleased. "But I don't think they'd touch your ship even if I wasn't here at all. It's simply too weird."

It took over two hours until the steady flow of petromites dwindled and stopped. By then, almost every surface in the room was covered with them, and combined with the pale green light, their glow made everything look eerie and enchanted.

"Everyone in?" the Doctor asked Jess and the queen.

The queen waggled her antennae as an affirmative.

Jess looked from the petromite to the Doctor, her light yellow eyes wide. "She understood you!"

"That's the TARDIS translating for me."

"No, it's more than that - they trust you, even though you're not Khiandrian. How's that possible?"

"I've got a very trustworthy face! Having some talent for telepathy helps, too."

"You're the strangest alien I've ever met," Jess proclaimed.

"Thank you!" the Doctor said, beaming.

Even though the number of passengers aboard the TARDIS was far greater than ever before, their flight to Khiandria was a quick and steady one. The landing was unusually smooth as well, as if she was careful to keep the petromites happy.

"That was it? We're on another planet now?" Grant asked disbelievingly.

Jess walked to the door, opened it, and sniffed at the air outside. "We are, indeed!" she declared. "Wait here, I'll go and make sure there are no gaping chasms next to the ship."

She returned almost instantly, a huge smile on her pale lips. "I don't know how you did it, but you've picked the perfect spot. You're going to love this," she told them. "Come on! There is actually a big drop nearby, but don't worry, there's a parapet."

It took the Doctor's eyes some time to adjust to the lighting outside the TARDIS, dim after the glow of the millions of petromites. After that, he needed another moment to actually grasp what he saw.

They had landed on a large viewing platform, up high in the largest cave chamber he had ever seen - it was at least the size of Cardiff. The gently curving ceiling was full of thin stalactites, translucent and glimmering. Hundreds of feet below them lay a city built of stone and crystal, its houses and towers and streets and plazas speckled with lights in all the colours of the rainbow. The traditional pale green was dominant, of course, but there were dozens of pastel blues and pinks and yellows, and mauve and silver and amber, and many shades that English had no words for.

"Welcome to the City of Lights," Jess announced solemnly.

"Is this your home?" Brian asked, his voice barely louder than a whisper, filled with wonder.

"No, I lived in the capital. It's much bigger, spans across lots of chambers, but it's nowhere near this spectacular. We used to come here every year during the Flood Festival, when I was little," she said. "Magnificent, isn't it?"

"It's the second most beautiful thing I've ever seen," he said.

"What's -" Jess began, fell silent, and grinned at Brian. "Right. Thank you, darling," she said, and kissed him on the lips.

"We're not in a hurry to go home, are we?" Grant asked, leaning on the parapet, clearly transfixed by the view. The childlike delight on his face made him look at least twenty years younger.

"Most definitely not, if you ask me," Joseph said.

"What do you think, Martha?" the Doctor said. "Should we let the Sixties wait a few more days?"

Martha smirked. "Well. I thought I'd seen enough caves to last a lifetime, but I guess I could handle a day or two in this one. You'd better get yourself a helmet, though."

* * *

**Author's Endnote: **And that's it, The End! With plenty of room for a sequel, of course, even though I'm not planning on writing one right now. Maybe some day. Thanks for reading, and extra thanks and hugs to all the loyal reviewers! I really enjoyed writing this story and sharing it with you. :)


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